feat: video rips and stray copies handle themselves (M498 #5439)

- The resolver also merges cross-release and mismatch groups where Lidarr
  maps exactly one copy: the others fulfil nothing, so removing them opens no
  hole (D-a rule 1). That covers a rip beside the clean copy on another
  release and a wrong-file import Lidarr holds unmapped. With two or more
  mapped copies each fulfils its own release and nothing is removed.
- A track whose file name carries a video-rip marker is held back from radio
  and the system mixes (tracks.source_verdict, migration 0077). It still plays
  when chosen. A renamed file is released; the operator's "fine" sticks.
- Suspect sources shows what was done to each track, with "This one is fine"
  and "Hold back again" (PUT /api/admin/library/suspect-sources/{id}).
- The Liked list prefers a copy that is not held back.

Replacing a rip that has no clean copy is left for the operator to decide.

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

internal/recommendation/shuffle.go

@@ -52,6 +52,12 @@ func RadioDiversityCaps(limit int) DiversityCaps {
 	return DiversityCaps{MaxPerArtist: artist, MaxPerAlbum: album}
 }
 
+// heldBack says whether the candidate is a video rip held back from radio
+// (M498 #5439): it plays when chosen, but radio does not choose it.
+func heldBack(c Candidate) bool {
+	return c.Track.SourceVerdict != nil && *c.Track.SourceVerdict == "suspect"
+}
+
 // Shuffle scores each candidate, sorts descending by score, and returns the
 // top `limit` candidates, preferring artist/album diversity. limit <= 0
 // returns nil; nil input returns nil. Pure — no IO, no global state beyond
@@ -61,7 +67,9 @@ func RadioDiversityCaps(limit int) DiversityCaps {
 // first takes candidates that fit under the caps, and the second fills any
 // remaining slots from those the first pass skipped, still in score order.
 // So the result holds min(limit, len(candidates)) either way — the caps
-// change WHICH tracks are chosen, never HOW MANY.
+// change WHICH tracks are chosen, never HOW MANY. (What is not a candidate at
+// all is dropped first: a held-back video rip, and a second copy of a song
+// already chosen from another release, M498.)
 //
 // That two-pass shape is the whole design, and a hard cap would have been
 // the easy mistake. Radio asks for 50 tracks by default and 200 at most; a
@@ -119,7 +127,7 @@ func Shuffle(
 		if len(out) == limit {
 			break
 		}
-		if repeat(s.c) {
+		if heldBack(s.c) || repeat(s.c) {
 			continue
 		}
 		overArtist := caps.MaxPerArtist > 0 && artistCount[s.c.Track.ArtistID] >= caps.MaxPerArtist