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, 4 insertions, 2 deletions

diff --git a/packages/meshbay-node/tests/test_stream_audio_transcode.py b/packages/meshbay-node/tests/test_stream_audio_transcode.py
index 5b1fc46..dde0df4 100644
--- a/packages/meshbay-node/tests/test_stream_audio_transcode.py
+++ b/packages/meshbay-node/tests/test_stream_audio_transcode.py
@@ -149,13 +149,14 @@ async def test_probe_video_reports_aac_regardless_of_source_audio_codec(tmp_path
     clip = tmp_path / "clip.mkv"
     _make_clip(clip, acodec="eac3", channels=6)
 
-    codec, duration, has_audio = await _probe_video(str(clip))
+    codec, duration, has_audio, width, height = await _probe_video(str(clip))
 
     assert has_audio is True
     assert duration > 0
     assert codec is not None
     assert "eac3" not in codec and "ec-3" not in codec
     assert "mp4a.40.2" in codec
+    assert (width, height) == (320, 240)
 
 
 async def test_probe_video_handles_no_audio_track(tmp_path):
@@ -167,8 +168,9 @@ async def test_probe_video_handles_no_audio_track(tmp_path):
         check=True, capture_output=True,
     )
 
-    codec, duration, has_audio = await _probe_video(str(clip))
+    codec, duration, has_audio, width, height = await _probe_video(str(clip))
 
     assert has_audio is False
     assert codec is not None and "," not in codec, \
         "no audio track must not produce a dangling ',' or a fake audio codec"
+    assert (width, height) == (320, 240)