feat: admin Suspect sources report, for files named like video rips (#5410)

Humanz turned out to be YouTube rips: "(Official Video)", "Visualizer", a
reaction video filed as a song, junk disc numbers (#5401). The library holds
about 200 more files named the same way. This report lists them, grouped by
folder like Missing files, with the markers each file name carries.

- GET /api/admin/library/suspect-sources: one marker list in Go builds both
  the Postgres ~* filter and each row's labels, so they cannot drift.
  Basename only; missing files are left out.
- Markers calibrated on the live library: "live in/at" dropped (real live
  albums), "reaction" narrowed (it caught "Chain Reaction").
- Admin tab "Suspect sources", read-only, loads as you scroll; a folder split
  across pages is joined back into one.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

internal/db/queries/tracks.sql

@@ -263,3 +263,39 @@ SELECT t.id,
 -- Total for the admin surface's badge and paging. Uses the same partial index
 -- (tracks_missing_since_idx) as the list above.
 SELECT COUNT(*) FROM tracks WHERE missing_since IS NOT NULL;
+
+-- name: ListSuspectSourceTracks :many
+-- The admin report of present tracks whose filename looks like a video rip
+-- (#5410): "(Official Video)", "[Audio]", "Visualizer" and the like.
+--
+-- pattern is built in Go (internal/api/admin_suspect_sources.go) from the
+-- same marker list that labels each row, so the filter and the labels cannot
+-- drift. It is matched against the basename only: a folder called "Reaction
+-- Sessions" says nothing about how a file was sourced.
+--
+-- Ordered by directory, like ListMissingTracks, so the handler's fold gets
+-- each folder as one contiguous run.
+SELECT t.id,
+       t.title,
+       t.file_path,
+       regexp_replace(t.file_path, '/[^/]*$', '') AS directory,
+       t.duration_ms,
+       t.disc_number,
+       t.track_number,
+       albums.id     AS album_id,
+       albums.title  AS album_title,
+       artists.id    AS artist_id,
+       artists.name  AS artist_name
+  FROM tracks t
+  JOIN albums  ON albums.id  = t.album_id
+  JOIN artists ON artists.id = t.artist_id
+ WHERE t.missing_since IS NULL
+   AND regexp_replace(t.file_path, '^.*/', '') ~* sqlc.arg(pattern)::text
+ ORDER BY directory, t.disc_number NULLS FIRST, t.track_number NULLS FIRST, t.title
+ LIMIT sqlc.arg(page_limit) OFFSET sqlc.arg(page_offset);
+
+-- name: CountSuspectSourceTracks :one
+-- Total for the report's paging; the same filter as the list above.
+SELECT COUNT(*) FROM tracks t
+ WHERE t.missing_since IS NULL
+   AND regexp_replace(t.file_path, '^.*/', '') ~* sqlc.arg(pattern)::text;