feat(api): capture contextual_likes on like during open play_event

Two new helpers in internal/playevents (CaptureContextualLikeIfPlaying,
SoftDeleteContextualLikes) called by both api and subsonic surfaces.
Like inserts a new contextual_likes row when LikeTrack actually
inserted (rows=1) AND there's an open play_event with a vector.
Unlike soft-deletes via deleted_at. Idempotent in both directions.

Subsonic wiring lands in the next commit.

internal/playevents/contextual_likes.go

@@ -0,0 +1,59 @@
+package playevents
+
+import (
+	"context"
+	"errors"
+	"log/slog"
+
+	"github.com/jackc/pgx/v5"
+	"github.com/jackc/pgx/v5/pgtype"
+
+	"git.fabledsword.com/bvandeusen/minstrel/internal/db/dbq"
+)
+
+// CaptureContextualLikeIfPlaying snapshots the user's currently-playing
+// session context into a new contextual_likes row. No-op if no open
+// play_event exists or its session_vector is NULL. Failures are logged
+// but never returned to the caller — contextual capture is best-effort
+// and must not break the like response.
+func CaptureContextualLikeIfPlaying(
+	ctx context.Context,
+	q *dbq.Queries,
+	userID, trackID pgtype.UUID,
+	logger *slog.Logger,
+) error {
+	event, err := q.GetOpenPlayEventForUser(ctx, userID)
+	if err != nil {
+		if errors.Is(err, pgx.ErrNoRows) {
+			return nil // no play in progress; nothing to capture
+		}
+		logger.Error("playevents: get open play_event", "err", err)
+		return nil // best-effort
+	}
+	if event.SessionVectorAtPlay == nil {
+		return nil // event predates this slice; no vector to snapshot
+	}
+	if err := q.InsertContextualLike(ctx, dbq.InsertContextualLikeParams{
+		UserID:        userID,
+		TrackID:       trackID,
+		SessionVector: event.SessionVectorAtPlay,
+		SessionID:     event.SessionID,
+	}); err != nil {
+		logger.Error("playevents: insert contextual_like", "err", err)
+		return nil
+	}
+	return nil
+}
+
+// SoftDeleteContextualLikes marks all currently-active contextual_likes
+// rows for (user, track) as deleted. Idempotent.
+func SoftDeleteContextualLikes(
+	ctx context.Context,
+	q *dbq.Queries,
+	userID, trackID pgtype.UUID,
+) error {
+	return q.SoftDeleteContextualLikesForUserTrack(ctx, dbq.SoftDeleteContextualLikesForUserTrackParams{
+		UserID:  userID,
+		TrackID: trackID,
+	})
+}