feat(server): scanner + DeleteTrackFile write library_changes

Wires sync.LogChange into the library mutation sites so /api/library/sync
reflects upserts and deletes.

Architectural pivot: LogChange's signature is now (ctx, dbq.DBTX, ...) so
it works with both *pgxpool.Pool and pgx.Tx. The scanner doesn't run
mutations in explicit transactions, so it pool-binds; delete.go matches.
Tx-bound callers (likes/playlists in subsequent commits) keep atomicity.

Also: sync.FormatUUID centralizes the pgtype.UUID → canonical string
conversion that both the scanner and the sync handler need; library_sync.go
now uses it instead of a local copy.

Best-effort logging on scanner failures (Warn, don't fail the scan): a
LogChange error after a successful upsert is rare and self-healing — the
next scan that touches the entity re-emits the change.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

internal/library/delete.go

@@ -12,6 +12,7 @@ import (
 	"github.com/jackc/pgx/v5/pgxpool"
 
 	"git.fabledsword.com/bvandeusen/minstrel/internal/db/dbq"
+	syncpkg "git.fabledsword.com/bvandeusen/minstrel/internal/sync"
 )
 
 // ErrTrackNotFound is returned when DeleteTrackFile is called with an id
@@ -48,5 +49,12 @@ func DeleteTrackFile(ctx context.Context, pool *pgxpool.Pool, trackID pgtype.UUI
 	if _, err := pool.Exec(ctx, "DELETE FROM tracks WHERE id = $1", trackID); err != nil {
 		return fmt.Errorf("delete row: %w", err)
 	}
+	// Log the change after the delete succeeds. Best-effort: a Warn-level
+	// failure here would leave the cache index orphaned on offline clients
+	// until the next scan touches the surrounding album.
+	if err := syncpkg.LogChange(ctx, pool, syncpkg.EntityTrack,
+		syncpkg.FormatUUID(trackID), syncpkg.OpDelete); err != nil {
+		return fmt.Errorf("log change: %w", err)
+	}
 	return nil
 }