refactor(api): TOML 配置 SSOT、统一错误契约、Auth/事务加固与可观测性 (#33)

配置 SSOT（TOML + .env）
统一错误契约
Auth 与事务边界
Redis / Celery 可靠性:业务 Redis（DB/0）与 Celery broker/backend（DB/1）显式拆分；连接池、sync client
可观测性（OpenTelemetry + LGTM）

api/.agents/skills/redis-development/rules/conn-pooling.md

@@ -0,0 +1,71 @@
+---
+title: Use Connection Pooling or Multiplexing
+impact: HIGH
+impactDescription: Reduces connection overhead by 10x or more
+tags: connections, pooling, multiplexing, performance
+description: Use Connection Pooling or Multiplexing
+alwaysApply: true
+---
+
+## Use Connection Pooling or Multiplexing
+
+Reuse connections via a pool or multiplexing instead of creating new connections per request.
+
+**Correct:** Use a connection pool.
+
+**Python** (redis-py):
+```python
+import redis
+
+# Good: Connection pool - reuses existing connections
+pool = redis.ConnectionPool(host='localhost', port=6379, max_connections=50)
+r = redis.Redis(connection_pool=pool)
+```
+
+**Java** (Jedis):
+```java
+import redis.clients.jedis.JedisPooled;
+
+// JedisPooled manages a connection pool internally
+try (JedisPooled jedis = new JedisPooled("redis://localhost:6379")) {
+    jedis.set("testKey", "testValue");
+}
+```
+
+**Correct:** Use multiplexing (Lettuce, NRedisStack).
+
+```java
+// Lettuce uses multiplexing by default - single connection handles all traffic
+RedisClient client = RedisClient.create("redis://localhost:6379");
+StatefulRedisConnection<String, String> connection = client.connect();
+
+// All commands share the single connection efficiently
+connection.sync().set("key", "value");
+```
+
+**Incorrect:** Creating new connections per request.
+
+**Python** (redis-py):
+```python
+# Bad: New connection every time
+def get_user(user_id):
+    r = redis.Redis(host='localhost', port=6379)  # Don't do this
+    return r.get(f"user:{user_id}")
+```
+
+**Java** (Jedis):
+```java
+// Bad: Creating new client per request
+public String getUser(String userId) {
+    try (UnifiedJedis jedis = new UnifiedJedis("redis://localhost:6379")) {
+        return jedis.get("user:" + userId);  // Don't do this
+    }
+}
+```
+
+**Pooling vs Multiplexing:**
+- **Pooling**: Multiple connections shared across requests (redis-py, Jedis, go-redis)
+- **Multiplexing**: Single connection handles all traffic (NRedisStack, Lettuce)
+- Multiplexing cannot support blocking commands (BLPOP, etc.) as they would stall all callers
+
+Reference: [Connection Pools and Multiplexing](https://redis.io/docs/latest/develop/clients/pools-and-muxing/)