refactor(saas): 架构重构 + 性能优化 — 借鉴 loco-rs 模式

Phase 0: 知识库
- docs/knowledge-base/loco-rs-patterns.md — loco-rs 10 个可借鉴模式研究

Phase 1: 数据层重构
- crates/zclaw-saas/src/models/ — 15 个 FromRow 类型化模型
- Login 3 次查询合并为 1 次 AccountLoginRow 查询
- 所有 service 文件从元组解构迁移到 FromRow 结构体

Phase 2: Worker + Scheduler 系统
- crates/zclaw-saas/src/workers/ — Worker trait + 5 个具体实现
- crates/zclaw-saas/src/scheduler.rs — TOML 声明式调度器
- crates/zclaw-saas/src/tasks/ — CLI 任务系统

Phase 3: 性能修复
- Relay N+1 查询 → 精准 SQL (relay/handlers.rs)
- Config RwLock → AtomicU32 无锁 rate limit (state.rs, middleware.rs)
- SSE std::sync::Mutex → tokio::sync::Mutex (relay/service.rs)
- /auth/refresh 阻塞清理 → Scheduler 定期执行

Phase 4: 多环境配置
- config/saas-{development,production,test}.toml
- ZCLAW_ENV 环境选择 + ZCLAW_SAAS_CONFIG 精确覆盖
- scheduler 配置集成到 TOML

crates/zclaw-saas/src/db.rs

@@ -4,7 +4,7 @@ use sqlx::postgres::PgPoolOptions;
 use sqlx::PgPool;
 use crate::error::SaasResult;
 
-const SCHEMA_VERSION: i32 = 4;
+const SCHEMA_VERSION: i32 = 5;
 
 const SCHEMA_SQL: &str = r#"
 CREATE TABLE IF NOT EXISTS saas_schema_version (
@@ -337,6 +337,11 @@ CREATE TABLE IF NOT EXISTS refresh_tokens (
 CREATE INDEX IF NOT EXISTS idx_refresh_account ON refresh_tokens(account_id);
 CREATE INDEX IF NOT EXISTS idx_refresh_jti ON refresh_tokens(jti);
 CREATE INDEX IF NOT EXISTS idx_refresh_expires ON refresh_tokens(expires_at);
+
+-- Performance: expression indexes for date-range queries on TEXT timestamp columns
+CREATE INDEX IF NOT EXISTS idx_usage_day ON usage_records((SUBSTRING(created_at, 1, 10)));
+CREATE INDEX IF NOT EXISTS idx_relay_day ON relay_tasks((SUBSTRING(created_at, 1, 10)));
+CREATE INDEX IF NOT EXISTS idx_relay_time ON relay_tasks(created_at);
 "#;
 
 const SEED_ROLES: &str = r#"
@@ -351,10 +356,11 @@ ON CONFLICT (id) DO NOTHING;
 /// 初始化数据库
 pub async fn init_db(database_url: &str) -> SaasResult<PgPool> {
     let pool = PgPoolOptions::new()
-        .max_connections(20)
-        .min_connections(2)
-        .acquire_timeout(std::time::Duration::from_secs(5))
-        .idle_timeout(std::time::Duration::from_secs(600))
+        .max_connections(50)
+        .min_connections(5)
+        .acquire_timeout(std::time::Duration::from_secs(10))
+        .idle_timeout(std::time::Duration::from_secs(300))
+        .max_lifetime(std::time::Duration::from_secs(1800))
         .connect(database_url)
         .await?;
 
@@ -387,7 +393,7 @@ pub async fn init_db(database_url: &str) -> SaasResult<PgPool> {
 
 /// 如果 accounts 表为空且环境变量已设置，自动创建 super_admin 账号
 /// 或者更新现有 admin 用户的角色为 super_admin
-async fn seed_admin_account(pool: &PgPool) -> SaasResult<()> {
+pub async fn seed_admin_account(pool: &PgPool) -> SaasResult<()> {
     let admin_username = std::env::var("ZCLAW_ADMIN_USERNAME")
         .unwrap_or_else(|_| "admin".to_string());