refactor: import brand icons directly from design-system package

- Sidebar and sign-in logos use Vite import from @cameleer/design-system
- HTML favicons copied by postinstall script (gitignored)
- Remove manually copied PNGs from repo
- Clean up SecurityConfig permitAll (bundled assets under /_app/**)

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

ui/src/components/Layout.tsx

@@ -8,11 +8,12 @@ import {
 import { useAuth } from '../auth/useAuth';
 import { useScopes } from '../auth/useScopes';
 import { EnvironmentTree } from './EnvironmentTree';
+import cameleerLogo from '@cameleer/design-system/assets/cameleer3-48.png';
 
 function CameleerLogo() {
   return (
     <img
-      src="/platform/cameleer-logo-48.png"
+      src={cameleerLogo}
       alt=""
       width="24"
       height="24"