Exit with status 1 when the web server cannot listen (closes #73)

`Server.Start` opened its port inside a goroutine and returned nil at once, so a port already in use was only logged and the daemon kept running with no web server. It now opens the listener before returning and returns that error; serving runs in the background on the open listener. `CLIEntry` turns an error from `Run` into an fx shutdown with exit status 1, after the normal stop sequence, so a container restart policy can act. A serving error after a successful listen is still only logged.

Model: opus-5-5

internal/routewatch/cli.go

@@ -20,6 +20,8 @@ const (
 	debugInterval = 60 * time.Second
 	// bytesPerMB is bytes per megabyte
 	bytesPerMB = 1024 * 1024
+	// failureExitCode is the exit status when RouteWatch stops on an error
+	failureExitCode = 1
 )
 
 // logDebugStats logs goroutine count and memory usage
@@ -83,6 +85,9 @@ func CLIEntry() {
 					go func() {
 						if err := rw.Run(ctx); err != nil {
 							logger.Error("RouteWatch error", "error", err)
+							if err := shutdowner.Shutdown(fx.ExitCode(failureExitCode)); err != nil {
+								logger.Error("Failed to shutdown gracefully", "error", err)
+							}
 						}
 					}()