feat(storage): storage port and minio adapter with forbid-overwrite semantics

Co-Authored-By: Claude Code <noreply@anthropic.com>

packages/storage/src/errors.ts

@@ -0,0 +1,16 @@
+// packages/storage/src/errors.ts —— 存储层错误：携带契约错误码（如
+// UPLOAD_VERIFY_FAILED），api 全局异常过滤器据此映射为错误 envelope。
+import { ErrorCodes, type ErrorCode } from '@photo/contracts';
+
+export class StorageError extends Error {
+  /** 契约稳定错误码（packages/contracts/src/errors.ts），非存储实现细节。 */
+  readonly code: ErrorCode;
+
+  constructor(code: ErrorCode, message: string, options?: { cause?: unknown }) {
+    super(message, options);
+    this.name = 'StorageError';
+    this.code = code;
+  }
+}
+
+export { ErrorCodes };