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/shared/hook-constants.ts

@@ -1,11 +1,12 @@
 export const HOOK_TIMEOUTS = {
   DEFAULT: 300000,            // Standard HTTP timeout (5 min for slow systems)
-  HEALTH_CHECK: 30000,        // Worker health check (30s for slow systems)
+  HEALTH_CHECK: 3000,         // Worker health check (3s — healthy worker responds in <100ms)
+  POST_SPAWN_WAIT: 5000,      // Wait for daemon to start after spawn (starts in <1s on Linux)
+  PORT_IN_USE_WAIT: 3000,     // Wait when port occupied but health failing
   WORKER_STARTUP_WAIT: 1000,
-  WORKER_STARTUP_RETRIES: 300,
   PRE_RESTART_SETTLE_DELAY: 2000,  // Give files time to sync before restart
   POWERSHELL_COMMAND: 10000,     // PowerShell process enumeration (10s - typically completes in <1s)
-  WINDOWS_MULTIPLIER: 1.5     // Platform-specific adjustment
+  WINDOWS_MULTIPLIER: 1.5     // Platform-specific adjustment for hook-side operations
 } as const;
 
 /**