feat(scanner): add folder hash for smarter quick scan change detection (#4220)

* Simplify folder hash migration

* fix hashing lint

* refactor

Signed-off-by: Deluan <deluan@navidrome.org>

* Update scanner/folder_entry.go

Co-authored-by: Copilot <175728472+Copilot@users.noreply.github.com>

---------

Signed-off-by: Deluan <deluan@navidrome.org>
Co-authored-by: Copilot <175728472+Copilot@users.noreply.github.com>

db/migrations/20250701010101_add_folder_hash.go

@@ -0,0 +1,21 @@
+package migrations
+
+import (
+	"context"
+	"database/sql"
+
+	"github.com/pressly/goose/v3"
+)
+
+func init() {
+	goose.AddMigrationContext(upAddFolderHash, downAddFolderHash)
+}
+
+func upAddFolderHash(ctx context.Context, tx *sql.Tx) error {
+	_, err := tx.ExecContext(ctx, `alter table folder add column hash varchar default '' not null;`)
+	return err
+}
+
+func downAddFolderHash(ctx context.Context, tx *sql.Tx) error {
+	return nil
+}