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/pages/login.js

@@ -16,7 +16,7 @@ import {
     handleLoginSuccess,
     webauthnSupported,
     startAuthentication,
-} from '/static/hoover/index.js?v=14';
+} from '/static/hoover/index.js';
 
 function LoginPage() {
     const hasWebAuthn = webauthnSupported();