fix(media_player): keep blank app names out of the source list (t49 F1)

t48 F1: source_list stringified the app map's values without filtering, so a
hand-edited map with a blank name ("com.x=") put an empty string in the dropdown.
That entry is worse than useless — it is a dropdown item whose only possible outcome
is an error, because select_source has to reject an empty name as an unknown source.

source_list now drops blank and whitespace-only names. The values themselves are
untouched: no name is rewritten or trimmed here, because the reverse lookup matches on
them, so for a well-formed map the list stays byte-equal to the Browse tree's child
titles (same _app_directory accessor, same order) — pinned by comparing the two
directly, for the user's map and for the curated default. The reverse lookup is
unchanged.

Tests (tests/test_media_sources.py, 3 new; tests/test_standalone_setup.py, 1 new):
a hand-edited map with "" and "   " entries offers only the real names; the offered
list equals the Browse tree titles for well-formed maps (both map and curated
default); the surviving entries still resolve AND launch through select_source, and a
blank name still resolves to nothing; and the editor keeps rejecting "com.x="
(_app_map_from_text returns None, the page answers invalid_app_map and stores nothing
half-way), so a blank name cannot get in that way either.

RED PROOF: with the filter removed, exactly the two blank-name tests fail — the blank
appears in the list, and the entry has no package to resolve to (1 passed / 2 failed;
the byte-equality test passes either way, which is the "well-formed list unchanged"
half of the claim) — while the rest of the file is green; restored, 20 pass.

Verified: 458 passed / 2 skipped, 459 / 1 with androidtvremote2, ruff clean, drift
engine exit 0 under real HA (23 modules, 58 imports, 164 relative imports, 36 call
arguments, 7 awaited HA calls).

Residual, deliberately NOT touched here (out of this repair's scope, and pre-existing):
a blank map entry still reaches the Browse tree as an empty child title, and a PADDED
name ("  TiviMate ", hand-edited only — the editor strips) still fails the reverse
lookup because the map value is matched unstripped. Both are hand-edited-map edges;
say the word and either can be a follow-up.

tests/test_media_sources.py

@@ -59,6 +59,54 @@ class TestSourceList:
 
         assert player.source_list == ["TiviMate", "Wholphin", "Netflix", "YouTube"]
 
+    def test_a_blank_name_never_reaches_the_dropdown(self, modules):
+        """t49: the map is hand-editable, so 'com.x=' must not offer an empty entry.
+
+        An empty entry is worst than useless: it is a dropdown item that
+        select_source has to reject as an unknown source.
+        """
+        player, _served = _player(
+            modules,
+            app_map={
+                "com.blank": "",
+                TIVIMATE: "TiviMate",
+                "com.spaces": "   ",
+                "com.netflix.ninja": "Netflix",
+            },
+        )
+
+        assert player.source_list == ["TiviMate", "Netflix"]
+        assert "" not in player.source_list
+
+    async def test_the_list_matches_the_browse_titles_exactly(self, modules):
+        """Same accessor, same order, same bytes — a blank entry excepted (t49)."""
+        for app_map in (
+            None,  # the curated default
+            {"ar.tvplayer.tv": "TiviMate", "com.netflix.ninja": "Netflix"},
+        ):
+            player, _served = _player(modules, app_map=app_map)
+
+            root = await player.async_browse_media()
+
+            assert player.source_list == [child.title for child in root.children]
+
+    async def test_the_survivors_still_resolve_and_launch(self, modules):
+        """The filter must not cost a resolvable name (t49)."""
+        player, _served = _player(
+            modules,
+            app_map={"com.blank": "", TIVIMATE: "TiviMate", "com.blank2": "  "},
+        )
+
+        for name in player.source_list:
+            assert player._source_package(name) is not None
+
+        await player.async_select_source("TiviMate")
+
+        assert player._manager._protocol.launch_calls == [TIVIMATE]
+        # the blank entries are not selectable, and never launch
+        assert player._source_package("") is None
+        assert player._source_package("   ") is None
+
     def test_every_offered_name_resolves_to_a_package(self, modules):
         """The invariant the shared directory buys: no name without a destination."""
         for app_map in (None, {"com.custom.one": "One"}):