feat(node,hub): add Videos group app (poster grid, flat list, TMDB metadata)

Implements docs/mediacenter.md: a "Videos" group application built on the
existing files index rather than a separate catalogue. On the node side,
new indexer enrichment (technical probe, filename/season parsing, thumbnail
generation) runs per-file once an operator has chosen a video_root for the
group, plus a TMDB client for on-demand poster/metadata lookups (never
client-side, thumbnails delivered over the existing chunk path). On the hub
side, a new video-app.js renders a lazily-mounted poster grid or a
thumbnail-only flat list, with TMDB entirely optional per group.

Along the way: the global apps registry now drives Settings' default-tab
picker instead of a hardcoded list, and the video_root is configured from
group Settings (like uploads) rather than from Files, with the node
refusing to run any TMDB/thumbnail work until one is set.

Fixes several bugs found via live testing against a real library, notably
a race between two effects writing the same "image ready" state that could
leave a poster grid spinning forever on a same-tab revisit — see
mediacenter.md §5.4 for the full account of each one.

1 files changed, 98 insertions, 0 deletions

diff --git a/packages/meshbay-node/tests/test_tmdb_language_fallback.py b/packages/meshbay-node/tests/test_tmdb_language_fallback.py
new file mode 100644
index 0000000..1a85531
--- /dev/null
+++ b/packages/meshbay-node/tests/test_tmdb_language_fallback.py
@@ -0,0 +1,98 @@
+"""
+TMDB doesn't fall back server-side for a field with no translation in the
+requested language — it returns "" (or an empty list) for that one field,
+not the English text, confirmed live against a real French query. The TMDB
+website itself covers exactly this gap client-side by falling back to
+English per field; `_tmdb_build_meta` (webrtc_server.py) mirrors that,
+rather than discarding an otherwise-good localized response over one empty
+field, or silently showing a blank overview/poster.
+"""
+
+import pytest
+
+from meshbay_node.transport.webrtc_server import WebRTCPeerSession
+
+pytestmark = pytest.mark.asyncio
+
+
+class FakeTmdbClient:
+    def __init__(self, localized: dict, english: dict, credits: dict | None = None):
+        self._localized = localized
+        self._english = english
+        self._credits = credits or {"cast": [], "crew": []}
+        self.calls: list[tuple[str, str | None]] = []
+
+    async def movie_details(self, tmdb_id, language=None):
+        self.calls.append(("movie_details", language))
+        return self._english if language == "en-US" else self._localized
+
+    async def tv_details(self, tmdb_id, language=None):
+        self.calls.append(("tv_details", language))
+        return self._english if language == "en-US" else self._localized
+
+    async def movie_credits(self, tmdb_id):
+        return self._credits
+
+    async def tv_credits(self, tmdb_id):
+        return self._credits
+
+
+async def test_empty_overview_falls_back_to_english_but_keeps_localized_poster():
+    localized = {
+        "title": "OVNI(s)", "original_title": "OVNI(s)",
+        "overview": "",  # no French translation on TMDB for this field
+        "poster_path": "/fr-poster.jpg", "backdrop_path": "/fr-backdrop.jpg",
+        "genres": [{"name": "Comédie"}], "vote_average": 7.2,
+        "first_air_date": "2016-01-01",
+    }
+    english = {
+        "title": "UFOs", "original_title": "OVNI(s)",
+        "overview": "A real English overview.",
+        "poster_path": "/en-poster.jpg", "backdrop_path": "/en-backdrop.jpg",
+        "genres": [{"name": "Comedy"}], "vote_average": 7.2,
+        "first_air_date": "2016-01-01",
+    }
+    client = FakeTmdbClient(localized, english)
+
+    meta = await WebRTCPeerSession._tmdb_build_meta(client, "108353", "tv", {"id": 108353})
+
+    assert meta["overview"] == "A real English overview.", (
+        "the empty localized field must fall back to the English value")
+    assert meta["poster_path"] == "/fr-poster.jpg", (
+        "a non-empty localized field must NOT be overwritten by the English fallback"
+    )
+    assert meta["genres"] == ["Comédie"], "localized genres were present — kept as-is"
+    assert ("tv_details", "en-US") in client.calls, "the fallback fetch must actually happen"
+
+
+async def test_fully_populated_localized_response_never_triggers_a_fallback_call():
+    localized = {
+        "title": "OVNI(s)", "overview": "Un résumé complet en français.",
+        "poster_path": "/fr-poster.jpg", "genres": [{"name": "Comédie"}],
+        "vote_average": 7.2,
+    }
+    client = FakeTmdbClient(localized, english={"overview": "should never be used"})
+
+    meta = await WebRTCPeerSession._tmdb_build_meta(client, "108353", "tv", {"id": 108353})
+
+    assert meta["overview"] == "Un résumé complet en français."
+    assert client.calls == [("tv_details", None)], (
+        "a fully translated response must not cost a second TMDB request")
+
+
+async def test_completely_untranslated_response_falls_back_entirely():
+    localized = {"overview": "", "poster_path": None, "genres": []}
+    english = {
+        "title": "UFOs", "original_title": "OVNI(s)",
+        "overview": "A real English overview.", "poster_path": "/en-poster.jpg",
+        "genres": [{"name": "Comedy"}], "vote_average": 7.2,
+        "release_date": "2016-01-01",
+    }
+    client = FakeTmdbClient(localized, english)
+
+    meta = await WebRTCPeerSession._tmdb_build_meta(client, "418517", "movie", {"id": 418517})
+
+    assert meta["overview"] == "A real English overview."
+    assert meta["poster_path"] == "/en-poster.jpg"
+    assert meta["genres"] == ["Comedy"]
+    assert meta["title"] == "UFOs"