fix(cursor): clean up PID file on startDaemon failure and improve daemon robustness

- Add removePidFile() in safeResolve on failure to prevent stale PIDs
- Only send SIGKILL in stopDaemon if SIGTERM wait loop exhausted
- Check isDaemonRunning before model fetch to avoid 5s timeout
- Add port validation unit tests for startDaemon

tests/unit/cursor/cursor-daemon.test.ts

@@ -13,6 +13,7 @@ import {
   isDaemonRunning,
   getDaemonStatus,
   stopDaemon,
+  startDaemon,
 } from '../../../src/cursor/cursor-daemon';
 
 // Test isolation
@@ -116,6 +117,26 @@ describe('removePidFile', () => {
   });
 });
 
+describe('startDaemon', () => {
+  it('rejects invalid port (0)', async () => {
+    const result = await startDaemon({ port: 0, model: 'test' });
+    expect(result.success).toBe(false);
+    expect(result.error).toContain('Invalid port');
+  });
+
+  it('rejects invalid port (65536)', async () => {
+    const result = await startDaemon({ port: 65536, model: 'test' });
+    expect(result.success).toBe(false);
+    expect(result.error).toContain('Invalid port');
+  });
+
+  it('rejects non-integer port', async () => {
+    const result = await startDaemon({ port: 3.14, model: 'test' });
+    expect(result.success).toBe(false);
+    expect(result.error).toContain('Invalid port');
+  });
+});
+
 describe('isDaemonRunning', () => {
   it('returns false when no daemon is running on port', async () => {
     // Use a port that should not have anything running