feat: Add Notification hook handler for formatting idle notifications

Format raw JSON IPC messages from workers/teammates into user-friendly
display instead of showing raw JSON to users.

Changes:
- Add notification.py hook handler to hookify plugin that formats
  idle_notification, status_update, and progress_update messages
- Update hookify hooks.json to include Notification event handler
- Add Pattern 11 documentation for formatting teammate idle notifications
- Add format-idle-notification.sh example script

Raw JSON input like:
  {"type":"idle_notification","from":"worker-1","timestamp":"..."}

Now displays as:
  ⏺ worker-1
    ⎿ Status is idle

Slack thread: https://anthropic.slack.com/archives/C07VBSHV7EV/p1765785226571409?thread_ts=1765776251.343939&cid=C07VBSHV7EV

plugins/hookify/hooks/hooks.json

@@ -44,6 +44,17 @@
           }
         ]
       }
+    ],
+    "Notification": [
+      {
+        "hooks": [
+          {
+            "type": "command",
+            "command": "python3 ${CLAUDE_PLUGIN_ROOT}/hooks/notification.py",
+            "timeout": 10
+          }
+        ]
+      }
     ]
   }
 }