fix: add spawnSync error logging and restore 5s timeout

- Check spawnSync result and log warning on failure via stderr
- Restore osascript timeout to 5000ms, increase hook deadline to 10s
  for sufficient headroom

hooks/hooks.json

@@ -297,7 +297,7 @@
             "type": "command",
             "command": "node \"${CLAUDE_PLUGIN_ROOT}/scripts/hooks/run-with-flags.js\" \"stop:desktop-notify\" \"scripts/hooks/desktop-notify.js\" \"standard,strict\"",
             "async": true,
-            "timeout": 5
+            "timeout": 10
           }
         ],
         "description": "Send macOS desktop notification with task summary when Claude responds"