fix: bundle favicon.svg in sign-in UI instead of cross-service fetch

The sign-in page is served by Logto, not the SaaS app. Referencing
/platform/favicon.svg required SecurityConfig permitAll and cross-service
routing. Instead, bundle favicon.svg directly in the sign-in UI dist
so Logto serves it at /favicon.svg.

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

ui/sign-in/src/SignInPage.tsx

@@ -56,7 +56,7 @@ export function SignInPage() {
       <Card className={styles.card}>
         <div className={styles.loginForm}>
           <div className={styles.logo}>
-            <img src="/platform/favicon.svg" alt="" className={styles.logoImg} />
+            <img src="/favicon.svg" alt="" className={styles.logoImg} />
             cameleer3
           </div>
           <p className={styles.subtitle}>{subtitle}</p>