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/render.js

@@ -5,12 +5,12 @@
  * batched re-render loop integration with reactivity.js.
  */
 
-import { requestUpdate, setCommitFn } from './reactivity.js?v=6';
+import { requestUpdate, setCommitFn } from './reactivity.js?v=7';
 import {
     _vnodeDom, createDom, getDom, patchNode, sweepDom,
     setMountFn, setUnmountFn,
-} from './vdom.js?v=6';
-import { mountComponent, unmountComponent } from './component.js?v=6';
+} from './vdom.js?v=7';
+import { mountComponent, unmountComponent } from './component.js?v=7';
 
 /** Container → previous root vnodes */
 export const _renderSlots = new Map();