feat(04-01): integrate notifications and focus mode into daemon

- Notifier + FocusTimer fields in Daemon, initialized in NewDaemon
- processHookEvent notifies on Working -> Needs Input only (D-01)
- Focus mode suppresses notifications when active (D-05)
- FocusArgs in protocol, "focus" handler in daemon
- CLI "vmux focus <minutes>" command
- Tests for all notification transitions and focus handler

daemon.go

@@ -168,6 +168,8 @@ type Daemon struct {
 	httpServer        *http.Server
 	lastHookTime      time.Time
 	mu                sync.Mutex // protects lastHookTime
+	notifier          Notifier
+	focus             *FocusTimer
 }
 
 // NewDaemon creates a daemon ready to start.
@@ -181,6 +183,8 @@ func NewDaemon(sockPath, procDir, claudeDir string, labels *LabelStore) *Daemon
 		pollInterval: 5 * time.Second,
 		stopCh:       make(chan struct{}),
 		hookPort:     3119,
+		notifier:     &ExecNotifier{},
+		focus:        &FocusTimer{},
 	}
 }
 
@@ -439,6 +443,15 @@ func (d *Daemon) handleConnection(conn net.Conn) {
 		}
 		writeResponse(conn, Response{OK: true})
 
+	case "focus":
+		var args FocusArgs
+		if err := json.Unmarshal(req.Args, &args); err != nil {
+			writeResponse(conn, Response{Error: "invalid focus args: " + err.Error()})
+			return
+		}
+		d.focus.Set(time.Duration(args.Minutes) * time.Minute)
+		writeResponse(conn, Response{OK: true, FocusRemaining: d.focus.Remaining().Minutes()})
+
 	case "stop":
 		writeResponse(conn, Response{OK: true})
 		d.Stop()