- server: reject Start() when config is nil to prevent panic
- app_common: guard empty Servers slice in initHTTP2/3 and logServerAddresses
- proxy/health: handle nil HealthCheckConfig with defaults
- resolver: handle nil ResolverConfig by returning noopResolver
- middleware/headers: skip UpdateConfig when cfg is nil
- middleware/sliding_window: enforce minimum window duration of 1s
- lua/api_log: map EMERG/ALERT/CRIT to Error() instead of Fatal()
to prevent Lua scripts from killing the entire server process
- Fix handleConnection to use addr parameter for direct upstream map
lookup instead of always selecting the first upstream
- Add Server.Stop() for graceful shutdown with listener closing, UDP
server cleanup, health checker termination, and goroutine joining
- Add shutdownStream() to App and call it in SIGTERM/SIGQUIT/SIGUSR2
signal handlers to prevent goroutine and port leaks on shutdown
