Add watchdog agent profile to command center

- Add 'watchdog' to KNOWN_PROFILES (5th agent)
- Custom status check via watchdog state file + kanban gateway fallback
- New /api/watchdog/status endpoint with scripts, plugins, heartbeat info
- Watchdog endpoint bypasses auth (public, non-sensitive)
- Update frontend PROFILE_ICONS + cache buster

static/index.html

@@ -286,7 +286,7 @@
 
         </main>
     </div>
-    <script src="/static/app.js?v=2"></script>
+    <script src="/static/app.js?v=3"></script>
     <script src="/static/vault.js?v=2"></script>
 </body>
 </html>