fix: hook resilience and worker lifecycle improvements (#957, #923, #984, #987, #1042)

Reduce timeouts to eliminate 10-30s startup delay when worker is dead
(common on WSL2 after hibernate). Add stale PID detection, graceful
error handling across all handlers, and error classification that
distinguishes worker unavailability from handler bugs.

- HEALTH_CHECK 30s→3s, new POST_SPAWN_WAIT (5s), PORT_IN_USE_WAIT (3s)
- isProcessAlive() with EPERM handling, cleanStalePidFile()
- getPluginVersion() try-catch for shutdown race (#1042)
- isWorkerUnavailableError: transport+5xx+429→exit 0, 4xx→exit 2
- No-op handler for unknown event types (#984)
- Wrap all handler fetch calls in try-catch for graceful degradation
- CLAUDE_MEM_HEALTH_TIMEOUT_MS env var override with validation

tests/hook-constants.test.ts

@@ -28,18 +28,22 @@ describe('hook-constants', () => {
       expect(HOOK_TIMEOUTS.DEFAULT).toBe(300000);
     });
 
-    it('should define HEALTH_CHECK timeout', () => {
-      expect(HOOK_TIMEOUTS.HEALTH_CHECK).toBe(30000);
+    it('should define HEALTH_CHECK timeout as 3s (reduced from 30s)', () => {
+      expect(HOOK_TIMEOUTS.HEALTH_CHECK).toBe(3000);
+    });
+
+    it('should define POST_SPAWN_WAIT as 5s', () => {
+      expect(HOOK_TIMEOUTS.POST_SPAWN_WAIT).toBe(5000);
+    });
+
+    it('should define PORT_IN_USE_WAIT as 3s', () => {
+      expect(HOOK_TIMEOUTS.PORT_IN_USE_WAIT).toBe(3000);
     });
 
     it('should define WORKER_STARTUP_WAIT', () => {
       expect(HOOK_TIMEOUTS.WORKER_STARTUP_WAIT).toBe(1000);
     });
 
-    it('should define WORKER_STARTUP_RETRIES', () => {
-      expect(HOOK_TIMEOUTS.WORKER_STARTUP_RETRIES).toBe(300);
-    });
-
     it('should define PRE_RESTART_SETTLE_DELAY', () => {
       expect(HOOK_TIMEOUTS.PRE_RESTART_SETTLE_DELAY).toBe(2000);
     });