feat: add macOS desktop notification Stop hook

Add a new Stop hook that sends a native macOS notification with the
task summary (first line of last_assistant_message) when Claude finishes
responding. Uses osascript via spawnSync for shell injection safety.
Supports run-with-flags fast require() path. Only active on standard
and strict profiles; silently skips on non-macOS platforms.

hooks/hooks.json

@@ -289,6 +289,18 @@
           }
         ],
         "description": "Track token and cost metrics per session"
+      },
+      {
+        "matcher": "*",
+        "hooks": [
+          {
+            "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
+          }
+        ],
+        "description": "Send macOS desktop notification with task summary when Claude responds"
       }
     ],
     "SessionEnd": [