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/cluster-read-replicas.md

@@ -0,0 +1,55 @@
+---
+title: Use Read Replicas for Read-Heavy Workloads
+impact: MEDIUM
+impactDescription: Scales read throughput without adding primary nodes
+tags: cluster, replicas, read-scaling, high-availability
+description: Use Read Replicas for Read-Heavy Workloads
+alwaysApply: true
+---
+
+## Use Read Replicas for Read-Heavy Workloads
+
+For read-heavy workloads, distribute reads across replicas to reduce load on primaries.
+
+**Correct:** Configure replica reads in Redis Cluster.
+
+```python
+from redis.cluster import RedisCluster
+
+rc = RedisCluster(
+    host='localhost',
+    port=6379,
+    read_from_replicas=True  # Distribute reads to replicas
+)
+
+# Writes go to primary
+rc.set("key", "value")
+
+# Reads can be served by replicas (eventually consistent)
+value = rc.get("key")
+```
+
+**Correct:** Use replica reads in standalone replication setup.
+
+```python
+from redis import Redis
+
+# Connect to primary for writes
+primary = Redis(host='primary-host', port=6379)
+
+# Connect to replica for reads
+replica = Redis(host='replica-host', port=6379)
+
+# Write to primary
+primary.set("key", "value")
+
+# Read from replica (eventually consistent)
+value = replica.get("key")
+```
+
+**Considerations:**
+- Replica reads are eventually consistent
+- Don't read from replicas for data that was just written
+- Use for read-heavy, slightly-stale-OK workloads (caches, analytics, dashboards)
+
+Reference: [Redis Replication](https://redis.io/docs/latest/operate/oss_and_stack/management/replication/)