fix(lifecycle): use ProcessLifecycle for coordinated shutdown

Replace per-Watcher SIGINT handlers with a single ProcessLifecycle.install()
in TsWatch.start(). This eliminates competing signal handler races that left
orphaned child processes. Add @push.rocks/smartexit as direct dependency.

ts/tswatch.classes.tswatch.ts

@@ -46,6 +46,14 @@ export class TsWatch {
   public async start() {
     logger.log('info', 'Starting tswatch with config-driven mode');
 
+    // Install global process lifecycle handlers (SIGINT, SIGTERM, etc.)
+    // This is the single authority for signal handling — no per-watcher handlers.
+    plugins.smartexit.ProcessLifecycle.install();
+    const exitInstance = new plugins.smartexit.SmartExit({ silent: true });
+    exitInstance.addCleanupFunction(async () => {
+      await this.stop();
+    });
+
     // Start server if configured
     if (this.config.server?.enabled) {
       await this.startServer();