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

main.go

@@ -6,6 +6,7 @@ import (
 	"log"
 	"os"
 	"path/filepath"
+	"strconv"
 	"strings"
 	"time"
 
@@ -100,6 +101,33 @@ func main() {
 		}
 		fmt.Println("Label set.")
 
+	case "focus":
+		if len(filteredArgs) < 2 {
+			fmt.Fprintf(os.Stderr, "Usage: vmux focus <minutes>\n")
+			os.Exit(1)
+		}
+		minutes, err := strconv.Atoi(filteredArgs[1])
+		if err != nil || minutes < 0 {
+			fmt.Fprintf(os.Stderr, "Error: invalid minutes %q\n", filteredArgs[1])
+			os.Exit(1)
+		}
+		if err := EnsureDaemon(sockPath); err != nil {
+			fmt.Fprintf(os.Stderr, "Error: %v\n", err)
+			os.Exit(1)
+		}
+		client := NewClient(sockPath)
+		focusArgs, _ := json.Marshal(FocusArgs{Minutes: minutes})
+		resp, err := client.Send(Request{Action: "focus", Args: focusArgs})
+		if err != nil {
+			fmt.Fprintf(os.Stderr, "Error: %v\n", err)
+			os.Exit(1)
+		}
+		if !resp.OK {
+			fmt.Fprintf(os.Stderr, "Error: %s\n", resp.Error)
+			os.Exit(1)
+		}
+		fmt.Printf("Focus mode: notifications suppressed for %d minutes\n", minutes)
+
 	case "stop":
 		client := NewClient(sockPath)
 		resp, err := client.Send(Request{Action: "stop"})
@@ -170,6 +198,7 @@ Commands:
   list              List active Claude Code sessions
   switch <query>    Switch to the workspace of the matching session
   label <id> <text> Assign a label to a session
+  focus <minutes>   Suppress notifications for N minutes
   stop              Stop the vmux daemon
   daemon            Run the daemon in foreground (used internally)