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/events.sql

@@ -48,3 +48,21 @@ SELECT * FROM play_events WHERE id = $1;
 INSERT INTO skip_events (user_id, track_id, session_id, skipped_at, position_ms)
 VALUES ($1, $2, $3, $4, $5)
 RETURNING *;
+
+-- name: ListRecentSessionTracks :many
+-- Returns up to $3 tracks in session $1 whose play_event started before
+-- $2, ordered newest-first. Used by playevents.RecordPlayStarted to
+-- build the session_vector for the just-inserted play_event.
+SELECT t.* FROM tracks t
+JOIN play_events pe ON pe.track_id = t.id
+WHERE pe.session_id = $1
+  AND pe.started_at < $2
+ORDER BY pe.started_at DESC
+LIMIT $3;
+
+-- name: UpdatePlayEventVector :exec
+-- Used right after InsertPlayEvent to populate session_vector_at_play
+-- once the vector has been computed.
+UPDATE play_events
+SET session_vector_at_play = $2
+WHERE id = $1;