Read Codex rate limits at startup so Status always shows them

internal/agents/manager.go

@@ -114,6 +114,7 @@ func New(st *store.Store, worktreeRoot, leadRoot, codexHome string) *Manager {
 		watchStop:    make(chan struct{}),
 	}
 	go m.signalLoop()
+	go m.readCodexRateLimit()
 	return m
 }