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/hoover/router.js

@@ -5,8 +5,8 @@
  * navigation).  Link component for client-side navigation.
  */
 
-import { reactive } from './reactivity.js?v=6';
-import { h } from './vdom.js?v=6';
+import { reactive } from './reactivity.js?v=7';
+import { h } from './vdom.js?v=7';
 
 /**
  * Hash-based router.