feat(files): implement file storage functionality with save, load, and list operations

internal/store/db.go

@@ -92,5 +92,13 @@ func (db *DB) VerifyRequirements(ctx context.Context) error {
 		return fmt.Errorf("embeddings table is missing — run migrations")
 	}
 
+	var hasStoredFiles bool
+	if err := db.pool.QueryRow(ctx, `select exists(select 1 from pg_tables where schemaname = 'public' and tablename = 'stored_files')`).Scan(&hasStoredFiles); err != nil {
+		return fmt.Errorf("verify stored_files table: %w", err)
+	}
+	if !hasStoredFiles {
+		return fmt.Errorf("stored_files table is missing — run migrations")
+	}
+
 	return nil
 }