feat(db): add session-vector capture queries; LikeTrack returns row count

ListRecentSessionTracks + UpdatePlayEventVector for the vector capture
path inside RecordPlayStarted. LikeTrack switches to :execrows so the
contextual-likes capture can detect insert vs already-exists. Existing
callers updated to ignore the count for now; later tasks consume it.

internal/db/queries/likes.sql

@@ -1,4 +1,4 @@
--- name: LikeTrack :exec
+-- name: LikeTrack :execrows
 INSERT INTO general_likes (user_id, track_id)
 VALUES ($1, $2)
 ON CONFLICT (user_id, track_id) DO NOTHING;