feat(ai): temporal worker for lesson plan workflow

- deploy temporal server (postgresql + auto-setup + ui) in docker-compose
- new temporal/ module: workflow + activities + worker manager
- convert lesson plan 4-step orchestration to temporal workflow
- activities wrap existing analyze/recommend/generate/prepare_review steps
- worker injects failover_chain/content_client/data_ana_client via module globals
- start() uses temporal client.start_workflow, falls back to asyncio in dev
- register temporal ports 7233/8085 in port-allocation

Implements M6.5 of v2.1 migration plan (ADR-030).

infra/security/secrets.example.env

@@ -55,3 +55,8 @@ ENCRYPTION_KEY=<replace-with-base64-32-byte-aes-key>
 # 生成：openssl rand -hex 32
 # 注意：Router 和所有子图必须使用相同的密钥
 ROUTER_AUTH_SECRET=<replace-with-32-char-router-auth-secret>
+
+# ---------- Temporal ----------
+# 用途：Temporal PostgreSQL 存储密码
+# 最小长度：24 字符
+TEMPORAL_POSTGRES_PASSWORD=<replace-with-24-char-temporal-password>