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/sign-in/src/SignInPage.tsx

@@ -1,5 +1,6 @@
 import { type FormEvent, useMemo, useState } from 'react';
 import { Card, Input, Button, Alert, FormField } from '@cameleer/design-system';
+import cameleerLogo from '@cameleer/design-system/assets/cameleer3-48.png';
 import { signIn } from './experience-api';
 import styles from './SignInPage.module.css';
 
@@ -56,7 +57,7 @@ export function SignInPage() {
       <Card className={styles.card}>
         <div className={styles.loginForm}>
           <div className={styles.logo}>
-            <img src="/cameleer-logo-48.png" alt="" className={styles.logoImg} />
+            <img src={cameleerLogo} alt="" className={styles.logoImg} />
             cameleer3
           </div>
           <p className={styles.subtitle}>{subtitle}</p>