fix: handle Windows taskkill errors in orphaned process cleanup

Wrap taskkill call in try/catch so one process failing to kill doesn't
abort cleanup of remaining processes.

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

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

src/services/worker-service.ts

@@ -448,7 +448,11 @@ export class WorkerService {
           logger.warn('SYSTEM', 'Skipping invalid PID', { pid });
           continue;
         }
+        try {
           execSync(`taskkill /PID ${pid} /T /F`, { timeout: 60000, stdio: 'ignore' });
+        } catch {
+          // Process may have already exited - continue cleanup
+        }
       }
     } else {
       for (const pid of pids) {