[v3] Fix: Vite server not cleaned up when build fails (#4436)

* fix: properly clean up Vite server when build fails

Ensures the Vite server process is terminated when a build fails
during 'wails3 dev', preventing port conflicts on subsequent runs.

Fixes #4403

🤖 Generated with [Claude Code](https://claude.ai/code)

Co-Authored-By: Claude <noreply@anthropic.com>

* fix: add defer for watcher cleanup and tidy up returns

- Add defer cleanup() to ensure resources are always freed
- Remove manual cleanup in error path since defer handles it
- Simplify error handling for better maintainability

Addresses feedback on PR #4436

* fix: prevent channel deadlock in watcher cleanup

- Separate cleanup logic from channel notification
- cleanup() only stops the engine
- signalCleanup() handles both cleanup and channel notification
- Prevents deadlock when function exits normally

---------

Co-authored-by: Claude <noreply@anthropic.com>

v3/UNRELEASED_CHANGELOG.md

@@ -24,6 +24,7 @@ After processing, the content will be moved to the main changelog and this file
 
 ## Fixed
 <!-- Bug fixes -->
+- Fix Vite server not being cleaned up when build fails (#4403)
 
 ## Deprecated
 <!-- Soon-to-be removed features -->

v3/internal/commands/watcher.go

@@ -35,17 +35,31 @@ func Watcher(options *WatcherOptions) error {
 	if err != nil {
 		return err
 	}
-	signalHandler := signal.NewSignalHandler(func() {
+	
+	// Setup cleanup function that stops the engine
+	cleanup := func() {
+		watcherEngine.Stop()
+	}
+	defer cleanup()
+	
+	// Signal handler needs to notify when to stop
+	signalCleanup := func() {
+		cleanup()
 		stopChan <- struct{}{}
-	})
+	}
+	
+	signalHandler := signal.NewSignalHandler(signalCleanup)
 	signalHandler.ExitMessage = func(sig os.Signal) string {
 		return ""
 	}
 	signalHandler.Start()
+	
+	// Start the engine
 	err = watcherEngine.Start()
 	if err != nil {
 		return err
 	}
+	
 	<-stopChan
 	return nil
 }