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

src/cli/handlers/session-complete.ts

@@ -16,7 +16,11 @@ import { logger } from '../../utils/logger.js';
 export const sessionCompleteHandler: EventHandler = {
   async execute(input: NormalizedHookInput): Promise<HookResult> {
     // Ensure worker is running
-    await ensureWorkerRunning();
+    const workerReady = await ensureWorkerRunning();
+    if (!workerReady) {
+      // Worker not available — skip session completion gracefully
+      return { continue: true, suppressOutput: true };
+    }
 
     const { sessionId } = input;
     const port = getWorkerPort();