refactor: introduce model layer for centralized data synchronization

Add hoover model.js as a central reactive store per subsystem, replacing
per-component data fetching with a single source of truth.

- Add hoover/model.js with modelRegister, modelFetch, and WS invalidation
- Refactor websocket.js to route messages to model refresh (drop per-component
  subscribe/unsubscribe)
- Simplify component.js by removing WS subscription management
- Add refresh option to apiSubmit, deprecate refactorLoad and checkAbort
- Rewrite all pages to use getModel() instead of inline data fetching
- Bootstrap model registrations in app.js
- Add GET /api/firewall/state endpoint
- Fix restart-services.sh restart order and add service health verification
- Update hoover.md docs with model layer architecture

webui/static/index.html

@@ -14,6 +14,6 @@
     </div>
   </div>
   <script>window.__WS_URL__ = "__WS_URL_PLACEHOLDER__"</script>
-  <script type="module" src="/static/app.js?v=6"></script>
+  <script type="module" src="/static/app.js?v=7"></script>
 </body>
 </html>