Remove query-string cache-busting from static assets

Drop ?v=N version pins from all JS imports and HTML <link>/<script> tags.
Cache invalidation is now handled solely by server-side cache-control headers.
Update docs and AGENTS.md accordingly.

webui/static/hoover/model.js

@@ -13,7 +13,7 @@
  *   collectLoadingModels(...models) — combine loading/refreshing/error
  */
 
-import { reactive } from './reactivity.js?v=9';
+import { reactive } from './reactivity.js';
 
 /** Registered models: name → { model, subsystem, fetch } */
 const _models = new Map();