fix(media_player,config_flow): close the batch review's O2 and O3 (t17)

Both observations from the t8-t12 batch review, settled by execution rather than
by argument.

O2 — WHICH STATES MAY CARRY A NOW-PLAYING ROW. The review read
`extra_state_attributes` and argued the row publishes the entity state verbatim,
so `now_playing_state: on` is reachable, while the README documents only
playing/paused/buffering/idle; t10's author had reported that `on` and `off`
publish no row at all. The probe settles both halves:

* the t10 account is true on the NATURAL ladder — `on` means no source reported a
  power or playback fact, and every tier that can produce a reading sets
  `reported = True` in the ladder, so the two cannot meet;
* the review is right about the RULE. It was "publish unless the state is off", an
  assumption nothing enforced: forcing the ladder to `on` (and to `standby`, which
  the README does not even mention) published `now_playing_state: on`/`standby`
  beside a real title.

So the rule is now explicit — `NOW_PLAYING_STATE_VALUES = ("playing", "paused",
"buffering", "idle")` — and a reading is dropped whole when the entity state is
anything else, exactly as `off` always dropped it. Nothing legitimate is lost: a
tier only ever answers in one of those four (`idle` for "reported, nothing
playing", which is where the foreground tier's remembered-playback bridge lands).
The README says the same thing in the table row and in prose, and
tests/test_now_playing_publication.py walks EVERY `MediaPlayerState` member with a
reading present (the four publish themselves; on/off/standby publish nothing),
then reads the four values back OUT OF THE README and compares them to the
constant, so code and docs cannot drift again.

O3 — A REJECTED APP PASTE NAMES ITS BAD LINES. The bulk paste was all-or-nothing
and reported a generic `invalid_app_map`, so a 30-row paste with one typo had to
be bisected by hand. `_app_map_parse` now returns `(map | None, problems)` where
each problem carries the 1-based line NUMBER, the line as the user typed it, and
why (empty/space-bearing package, empty name, space in the icon), and the
rejection puts them in the form's `description_placeholders["invalid_lines"]`,
which the error copy interpolates — capped at 4 named lines with the remaining
count, so the message stays readable. The map is still None when anything is
wrong (never half-stored) and the detail is cleared as soon as a paste parses.
The single-row editor is untouched and keeps its own `invalid_app_row`; a test
asserts the new per-line report and `_valid_app_row` accept and refuse the same
rows, so a paste and a typed row cannot disagree.

Verify: 794 passed / 4 skipped, 795 passed / 3 skipped (with androidtvremote2),
ruff clean.

tests/test_now_playing_publication.py

@@ -0,0 +1,175 @@
+"""tests/test_now_playing_publication.py — which entity states may carry a reading (t17/O2).
+
+THE OBSERVATION THIS CLOSES. The batch review read `extra_state_attributes` and
+argued the now-playing row publishes "the entity state verbatim", so a dashboard
+could see `now_playing_state: on`, while the README documents only `playing`,
+`paused`, `buffering` and `idle`. t10's author had reported the opposite (an
+`on` or `off` device publishes no row at all). Both accounts were about a
+different thing, and this file settles it BY EXECUTION:
+
+* the t10 account is true for the NATURAL ladder — `on` means no source reported
+  a power or playback fact, and a reading only exists when a tier answered, so
+  the two cannot meet in practice;
+* the review was right about the RULE, which was "publish unless the state is
+  `off`" — an unenforced assumption, and the probe below shows it publishing
+  `now_playing_state: on` (and `standby`) the moment a reading exists beside that
+  state. `standby` is not even in the README, and nothing in the code stopped it.
+
+WHAT WAS CHANGED. The publication rule now names the four values a reading may
+carry (`NOW_PLAYING_STATE_VALUES`) and drops the reading when the entity state is
+anything else, exactly as a state of `off` always did. The README says the same
+thing in words. The two tests here walk EVERY ``MediaPlayerState`` member and
+compare the README against the code constant, so neither can drift again.
+"""
+
+from __future__ import annotations
+
+import re
+import sys
+from pathlib import Path
+
+sys.path.insert(0, str(Path(__file__).resolve().parent))
+import entity_stublib  # noqa: E402
+import pytest  # noqa: E402
+from entity_stublib import MediaPlayerState, load_entity_modules  # noqa: E402
+
+
+@pytest.fixture(autouse=True)
+def scoped_entity_stubs():
+    """Container for the HA stubs + the loaded entity modules (t7 discipline)."""
+    snapshot = entity_stublib.snapshot_modules()
+    entity_stublib.install()
+    yield load_entity_modules()
+    entity_stublib.restore_modules(snapshot)
+
+
+README = Path(__file__).resolve().parent.parent / "README.md"
+
+#: The states the README documents, read from the file itself (never from the
+#: constant under test) so a code change cannot silently rewrite the pin.
+def _documented_states() -> set[str]:
+    text = README.read_text(encoding="utf-8")
+    row = re.search(r"^\| `now_playing_state` \|(.*)\|$", text, re.M)
+    assert row, "the README's now_playing_state table row is gone"
+    return {value for value in re.findall(r"`([a-z_]+)`", row.group(1)) if value != "on"}
+
+
+def _player_for_state(modules, member):
+    """A player whose ladder answers `member` while a reading is available.
+
+    The state is forced by patching the ``state`` property, which is the only way
+    to ask "what would be published IF the ladder ever answered this?" — the
+    question the review raised. A reading is genuine: the foreground tier answers
+    it through the same code path production uses (``_now_playing``).
+    """
+    from test_command_routing import TIVIMATE_PACKAGE, _now_playing_attrs, _state_player
+
+    player, _manager = _state_player(modules, foreground=TIVIMATE_PACKAGE)
+    player._last_channel = "101"
+    media_player_cls = type(player)
+    original = media_player_cls.__dict__.get("state")
+    media_player_cls.state = property(lambda self, forced=member: forced)
+    try:
+        reading = player._now_playing()
+        attrs = _now_playing_attrs(player)
+    finally:
+        if original is None:  # pragma: no cover - the class always declares it
+            del media_player_cls.state
+        else:
+            media_player_cls.state = original
+    return reading, attrs
+
+
+class TestThePublicationRule:
+    """One reading in, one row out — for EVERY member the enum has."""
+
+    def test_the_documented_four_publish_the_reading(self, scoped_entity_stubs):
+        modules = scoped_entity_stubs
+        documented = {
+            MediaPlayerState.PLAYING: "playing",
+            MediaPlayerState.PAUSED: "paused",
+            MediaPlayerState.BUFFERING: "buffering",
+            MediaPlayerState.IDLE: "idle",
+        }
+
+        for member, value in documented.items():
+            reading, attrs = _player_for_state(modules, member)
+
+            assert reading, f"{value}: the fixture must have a reading to publish"
+            assert attrs["now_playing_state"] == value
+            assert attrs["now_playing_title"] == "101"
+
+    def test_a_state_outside_the_documented_four_publishes_nothing(self, scoped_entity_stubs):
+        """The review's case, executed: `on` publishes no row — by construction now."""
+        modules = scoped_entity_stubs
+        reading_available = {
+            MediaPlayerState.ON: "on",
+            MediaPlayerState.OFF: "off",
+            MediaPlayerState.STANDBY: "standby",
+        }
+
+        for member, value in reading_available.items():
+            reading, attrs = _player_for_state(modules, member)
+
+            assert reading, f"{value}: the fixture still HAS a reading (that is the point)"
+            assert attrs == {}, f"{value} must publish no now-playing row, got {attrs}"
+
+    def test_every_enum_member_is_accounted_for(self, scoped_entity_stubs):
+        """The matrix is exhaustive: no state is left untested as the enum grows."""
+        modules = scoped_entity_stubs
+        published = {}
+        for member in MediaPlayerState:
+            reading, attrs = _player_for_state(modules, member)
+            published[member.value] = attrs.get("now_playing_state")
+
+        assert set(published) == {member.value for member in MediaPlayerState}
+        for value in ("playing", "paused", "buffering", "idle"):
+            assert published[value] == value
+        for value in ("on", "off", "standby"):
+            assert published[value] is None, f"{value} published a state: {published[value]}"
+
+    def test_the_gate_reads_the_named_constant(self, scoped_entity_stubs):
+        """The rule is the constant, not a hard-coded pair of states."""
+        from nsh.media_player import NOW_PLAYING_STATE_VALUES
+
+        assert NOW_PLAYING_STATE_VALUES == ("playing", "paused", "buffering", "idle")
+        assert self._published_for(scoped_entity_stubs, MediaPlayerState.ON) == {}
+
+    @staticmethod
+    def _published_for(modules, member) -> dict:
+        _reading, attrs = _player_for_state(modules, member)
+        return attrs
+
+
+class TestTheReadmeAgrees:
+    """The docs and the code say the same four values (t17/O2's anti-drift pin)."""
+
+    def test_the_table_row_lists_exactly_the_constant(self, scoped_entity_stubs):
+        from nsh.media_player import NOW_PLAYING_STATE_VALUES
+
+        assert _documented_states() == set(NOW_PLAYING_STATE_VALUES)
+
+    def test_the_prose_names_the_same_set_and_excludes_on(self, scoped_entity_stubs):
+        text = README.read_text(encoding="utf-8")
+        from nsh.media_player import NOW_PLAYING_STATE_VALUES
+
+        paragraph = re.search(
+            r"\*\*`now_playing_state` is one of FOUR values[^*]*\*\*(.*?)\n-", text, re.S
+        )
+        assert paragraph, "the README's now_playing_state paragraph is gone"
+        body = paragraph.group(1)
+        # the sentence that names the set, read apart from the sentence that
+        # excludes `on`/`off` — otherwise the exclusion would look like a member
+        sentence = re.search(r"full set is ([^.]+)\.", body)
+        assert sentence, "the README no longer names the full set"
+        named = set(re.findall(r"`([a-z_]+)`", sentence.group(1)))
+        assert named == set(NOW_PLAYING_STATE_VALUES), named
+        assert "`on`" in body and "not one of them" in text, (
+            "the paragraph must say `on` is excluded"
+        )
+
+    def test_the_off_and_on_prose_still_says_no_rows(self, scoped_entity_stubs):
+        text = README.read_text(encoding="utf-8")
+
+        assert "**A device that reads `off` publishes none of them.**" in text
+        assert "publishes none either" in text