refactor(config): one Shield IP field for both transports (t41)

The two address fields were the same Shield spelled twice, and every bug in the
zeroconf/IP-change path came from keeping them in sync. One field now:

* const.CONF_HOST replaces CONF_ADB_HOST / CONF_PROTOCOL_HOST in the setup form,
  the options page, the pairing forms, the reconfigure/reauth seeding and the
  description copy. ADB port 5555 stays the only port field;
* helpers.entry_host(entry) is the single resolver (options first, then data);
  resolve_adb_config and the protocol settings both go through it, so both
  transports read the same value at call time (the t32 F1 factory re-read keeps
  working: the NEXT built poller sees the new address);
* helpers.seed_host / seed_adb_enabled own the YAML seed's shape rule. A block
  may use `host` or the legacy protocol_host/adb_host keys — t41 keeps the old
  spelling working — and t32 F4's outcome is unchanged: a protocol-only block
  leaves ADB off, an address (or an explicit adb_enabled) turns it on;
* the zeroconf IP-change path collapses the t21-F2 per-host dance into one rule:
  the discovery address IS the entry's address, so the entry is updated when it
  differs and left alone when it matches. The blank-self-heal and
  deliberately-different-ADB-host cases are gone with the duplication — a
  second address field cannot express them anymore, and the tests now pin that
  (previously "an explicit override is never clobbered");
* the options page exposes the protocol toggle it never had (the page could turn
  ADB off but not the protocol);
* button.py (granted to this task) reads the entry's own address instead of
  another integration's entity.

The v3 entry migration that maps existing adb_host/protocol_host onto CONF_HOST
and drops the androidtv key lands in the next commit; HA runs migrations before
setup, so an existing entry is never read with the old shape.

Verified: 311 passed / 2 skipped, 312 / 1 with androidtvremote2, ruff clean,
drift engine exit 0 on HEAD. The UI-copy contract tests (every rendered field
has a label in strings.json AND translations/en.json, key trees identical, host
errors name the field) drove the string edits.

tests/test_config_flow_protocol.py

@@ -15,15 +15,13 @@ import pytest
 from conftest import _SHIELD_DIR, _load_module
 from nsh.const import (
     CONF_ADB_ENABLED,
-    CONF_ADB_HOST,
     CONF_ADB_PORT,
     CONF_ADB_STORE_APP_INFO,
-    CONF_ANDROIDTV_ENTITY,
+    CONF_HOST,
     CONF_JELLYFIN_ENTITY,
     CONF_PAIRING_CODE,
     CONF_POWER_ENTITY,
     CONF_PROTOCOL_ENABLED,
-    CONF_PROTOCOL_HOST,
     CONF_RECEIVER_ENTITY,
     CONF_RECEIVER_INPUT,
     DEFAULT_ADB_PORT,
@@ -296,17 +294,15 @@ def make_flow(tmp_dir: str, monkeypatch: pytest.MonkeyPatch, client: FakeProtoco
     flow.hass = FakeHass(tmp_dir)
     flow._user_data = {
         "name": "mdarcy",
-        CONF_ANDROIDTV_ENTITY: "media_player.shield",
         CONF_JELLYFIN_ENTITY: "",
         CONF_RECEIVER_ENTITY: "",
         CONF_RECEIVER_INPUT: "",
         CONF_POWER_ENTITY: "",
         CONF_ADB_ENABLED: False,
         CONF_ADB_STORE_APP_INFO: True,
-        CONF_ADB_HOST: "",
+        CONF_HOST: "shield.local",  # t41: ONE address field
         CONF_ADB_PORT: DEFAULT_ADB_PORT,
         CONF_PROTOCOL_ENABLED: True,
-        CONF_PROTOCOL_HOST: "shield.local",
     }
     from nsh.connection import ShieldConnectionManager
 
@@ -350,7 +346,7 @@ class TestProtocolPairing:
         assert client.disconnected == 1
         assert result["type"] == "create_entry"
         assert result["options"][CONF_PROTOCOL_ENABLED] is True
-        assert result["options"][CONF_PROTOCOL_HOST] == "shield.local"
+        assert result["options"][CONF_HOST] == "shield.local"
 
     async def test_wrong_code_asks_again_then_succeeds(self, tmp_path, monkeypatch):
         client = FakeProtocolClient()
@@ -374,7 +370,7 @@ class TestReauthFlow:
         flow = make_flow(str(tmp_path), monkeypatch, client)
         entry = SimpleNamespace(
             entry_id="e1", title="mdarcy",
-            options={CONF_PROTOCOL_ENABLED: True, CONF_PROTOCOL_HOST: "shield.local"},
+            options={CONF_PROTOCOL_ENABLED: True, CONF_HOST: "shield.local"},
             data={},
         )
         flow.hass.config_entries.__dict__["__entry_e1"] = entry
@@ -411,9 +407,10 @@ class TestEntryMigration:
         # ADB options carried over byte-compatibly
         assert entry.options["adb_enabled"] is True
         assert entry.options["adb_port"] == 5555
-        # Protocol fields default; host discovery (ADB fallback) stays active
+        # Protocol fields default; the entry keeps its own address (t41: the v1
+        # adb_host is mapped onto CONF_HOST, empty here)
         assert entry.options[CONF_PROTOCOL_ENABLED] is False
-        assert entry.options[CONF_PROTOCOL_HOST] == ""
+        assert entry.options[CONF_HOST] == ""
         assert hass.config_entries.updating_entry_calls == [
             (entry, {"options": entry.options, "version": 2})
         ]