fix(lifecycle): use process group kill (-pid) in handleExit safety net

With detached:true children, the synchronous exit handler must kill
the entire process group, not just the direct PID.

ts/smartexit.classes.lifecycle.ts

@@ -187,18 +187,25 @@ export class ProcessLifecycle {
     });
   }
 
-  /** Synchronous last-resort: SIGKILL any remaining tracked PIDs. */
+  /** Synchronous last-resort: SIGKILL any remaining tracked process groups. */
   private handleExit(): void {
     const instances = ProcessLifecycle.getInstances();
     let killed = 0;
 
     for (const instance of instances) {
       for (const pid of instance.trackedPids) {
+        // Kill entire process group (negative PID) for detached children
         try {
-          process.kill(pid, 'SIGKILL');
+          process.kill(-pid, 'SIGKILL');
           killed++;
         } catch {
-          // Process already dead
+          // Process group may not exist, try single PID
+          try {
+            process.kill(pid, 'SIGKILL');
+            killed++;
+          } catch {
+            // Process already dead
+          }
         }
       }
     }