fix(media_player): D1 — browse builds real BrowseMedia nodes, not BrowseMediaSource (t37)

`homeassistant.components.media_player` has not exported `BrowseMediaSource`
for years: the class lives in `homeassistant.components.media_source.models`,
where it exists to build `media_source://<domain>` ids and is the only place a
`domain` parameter belongs (t30 G18's note was about THAT class). The local
import therefore raised ImportError, and with it every real browse failed —
while the suite stayed green because the harness stubbed a `BrowseMediaSource`
that real HA does not expose from there.

`async_browse_media` now builds the standard tree exactly as core's own
androidtv_remote/media_player.py does: `BrowseMedia` imported from
homeassistant.components.media_player at module scope, every node carrying an
explicit media_content_id/media_content_type (MediaType.APP/APPS),
`children_media_class=MediaClass.APP` on the directory, and no `domain`.
Verified against a real install: the old import raises ImportError, the old
`domain=` kwarg raises TypeError, and the new node constructs.

The harness is now faithful so this cannot hide again:
* `entity_stublib` exposes a `BrowseMedia` with the real keyword-only
  signature, `as_dict()` and `calculate_children_class()`, plus `MediaType`,
  and deliberately NOT `BrowseMediaSource` — so both the drifted import and the
  drifted kwarg fail in-suite;
* the app-directory test asserts the standard shape (classes, explicit ids and
  types, children_media_class, the serialised payload) instead of the removed
  `domain` attribute;
* TestFaithfulHaStubs pins the harness contract on the AST (no production
  module imports BrowseMediaSource) rather than on prose.

Verified: 284 passed, 2 skipped (D1 stage); ruff clean. Full gate re-run on the
completed branch: 289 passed / 2 skipped and 290 passed / 1 skipped.

custom_components/nvidia_shield/media_player.py

@@ -26,10 +26,13 @@ import time
 
 import voluptuous as vol
 from homeassistant.components.media_player import (
+    BrowseMedia,
+    MediaClass,
     MediaPlayerDeviceClass,
     MediaPlayerEntity,
     MediaPlayerEntityFeature,
     MediaPlayerState,
+    MediaType,
 )
 from homeassistant.config_entries import ConfigEntry
 from homeassistant.const import STATE_PAUSED, STATE_PLAYING
@@ -961,36 +964,40 @@ class NvidiaShieldMediaPlayer(MediaPlayerEntity):
     # ── BrowseMedia app directory (P4-2c) ──
 
     async def async_browse_media(self, media_content_type=None, media_content_id=None):
-        """Root lists the apps map (or the curated default) → play_media(app)."""
-        from homeassistant.components.media_player import (
-            BrowseMediaSource,
-            MediaClass,
-        )
+        """Root lists the apps map (or the curated default) → play_media(app).
 
+        t37 D1: the standard media_player tree, exactly as core's own
+        androidtv_remote/media_player.py builds it — ``BrowseMedia`` from
+        homeassistant.components.media_player, every node carrying an explicit
+        media_content_id/media_content_type, and the directory naming the
+        class of its children. ``BrowseMediaSource`` only ever existed in
+        homeassistant.components.media_source.models (t30 G18's domain
+        parameter is ITS contract: it builds ``media_source://<domain>`` ids),
+        so an app-directory node must never claim one — and the import above
+        removed a name media_player has not exported for a long time, which
+        made every real browse raise.
+        """
         app_map = self._entry.options.get(CONF_APP_NAME_MAP) or DEFAULT_APP_DIRECTORY
-        # G18 (2026-05-20 blog): BrowseMediaSource must carry the domain
-        # parameter so the frontend can attribute the media tree.
         children = [
-            BrowseMediaSource(
+            BrowseMedia(
                 title=name,
                 media_class=MediaClass.APP,
-                media_content_type="app",
+                media_content_type=MediaType.APP,
                 media_content_id=pkg,
                 can_play=True,
                 can_expand=False,
-                domain=DOMAIN,
             )
             for pkg, name in app_map.items()
         ]
-        return BrowseMediaSource(
+        return BrowseMedia(
             title="Apps",
             media_class=MediaClass.DIRECTORY,
-            media_content_type="apps",
+            media_content_type=MediaType.APPS,
             media_content_id="apps",
+            children_media_class=MediaClass.APP,
             can_play=False,
             can_expand=True,
             children=children,
-            domain=DOMAIN,
         )
 
     # ── play_media (§7): channel digits, app/url launch ──