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>

src/main/java/net/siegeln/cameleer/saas/config/SecurityConfig.java

@@ -45,7 +45,7 @@ public class SecurityConfig {
                         .requestMatchers("/api/config").permitAll()
                         .requestMatchers("/", "/index.html", "/login", "/callback",
                                 "/environments/**", "/license", "/admin/**").permitAll()
-                        .requestMatchers("/_app/**", "/favicon.ico", "/favicon.svg", "/favicon-32.png", "/favicon-192.png", "/cameleer-logo-48.png", "/logo.svg", "/logo-dark.svg").permitAll()
+                        .requestMatchers("/_app/**", "/favicon.ico", "/favicon-32.png", "/favicon-192.png", "/logo.svg", "/logo-dark.svg").permitAll()
                         .anyRequest().authenticated()
                 )
                 .oauth2ResourceServer(oauth2 -> oauth2.jwt(jwt ->