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.plugins.ts

@@ -16,6 +16,7 @@ import * as lik from '@push.rocks/lik';
 import * as npmextra from '@push.rocks/npmextra';
 import * as smartcli from '@push.rocks/smartcli';
 import * as smartdelay from '@push.rocks/smartdelay';
+import * as smartexit from '@push.rocks/smartexit';
 import * as smartfs from '@push.rocks/smartfs';
 import * as smartinteract from '@push.rocks/smartinteract';
 import * as smartlog from '@push.rocks/smartlog';
@@ -29,6 +30,7 @@ export {
   npmextra,
   smartcli,
   smartdelay,
+  smartexit,
   smartfs,
   smartinteract,
   smartlog,