feat(api): idempotent upload session init with presigned credential

POST /v1/uploads (Task 18, A03): @@unique(userId, clientTaskId) idempotency
anchor — same params return the original session (201, no duplicate photo);
param drift (album/bytes/contentType/extension) -> 409 UPLOAD_SESSION_CONFLICT.
photos.objectKey is set to the FINAL originals key at init while the session
holds the staging key; IDs come from an app-side cuid-like generator so both
self-referencing keys are written in one transaction. Credential is a real
MinIO presigned PUT (SIGNED_URL_TTL_SECONDS, lazily read). Permission order:
album invisible 404 -> member 403 -> uploadEnabled 409 -> size/ext 400 ->
category ownership 400. No audit on init (audit anchors on complete).

Pre-step for Task 19: QUEUE_PHOTO_PROCESS contract constant + lazy-safe
BullMQ queue producer (Redis down at boot must not crash the app; enqueue
failure only logs — sweep compensates). e2e reset now also wipes the MinIO
photo-live/dev prefix; jest maps @photo/storage to TS source.

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

packages/contracts/src/index.ts

@@ -2,6 +2,7 @@
 // 契约统一出口：错误码 + OpenAPI 生成类型（src/generated/openapi.d.ts 提交入库，
 // 消费方不跑 gen；本包改动后执行 pnpm gen 并提交生成文件 diff）。
 // NodeNext + ESM：相对导入必须带 .js 扩展名；生成文件仅含类型，用 export type * 在运行时擦除。
+export * from './constants.js';
 export * from './errors.js';
 export * from './events.js';
 export type * from './generated/openapi.js';