perf(db): tune sqlite pool and add maintenance scheduler

.env.example

@@ -18,6 +18,17 @@ SESSION_COOKIE_SECURE=false  # 使用HTTPS时设为true
 # ==================== 数据库配置 ====================
 DB_FILE=data/app_data.db
 DB_POOL_SIZE=5
+DB_CONNECT_TIMEOUT_SECONDS=10
+DB_BUSY_TIMEOUT_MS=10000
+DB_CACHE_SIZE_KB=8192
+DB_WAL_AUTOCHECKPOINT_PAGES=1000
+DB_MMAP_SIZE_MB=256
+DB_LOCK_RETRY_COUNT=3
+DB_LOCK_RETRY_BASE_MS=50
+DB_PRAGMA_OPTIMIZE_INTERVAL_SECONDS=21600
+DB_ANALYZE_INTERVAL_SECONDS=86400
+DB_WAL_CHECKPOINT_INTERVAL_SECONDS=43200
+DB_WAL_CHECKPOINT_MODE=PASSIVE
 
 # ==================== 并发控制配置 ====================
 MAX_CONCURRENT_GLOBAL=2