feat(hackathon): improve auth flow and UX

- Add email activation requirement for signup (no auto-login)
- Add form validation with React Hook Form and Zod on signup page
- Update callback page to handle email confirmation and password reset redirects
- Fix token format in API interceptor (use access_token)
- Fix middleware to use SessionToken for auth check
- Add infinite scroll with IntersectionObserver on browse teams page
- Replace all internal <a href> with <Link> components
- Add useInfiniteTeams hook for paginated team browsing

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude <noreply@anthropic.com>

libs/service/src/api/hackathon.ts

@@ -16,8 +16,8 @@ export const hackathonApi = axios.create({
 hackathonApi.interceptors.request.use(
   (config) => {
     const { session } = useAuthStore.getState();
-    if (session?.token) {
-      config.headers.Authorization = `Bearer ${session.token}`;
+    if (session?.token?.access_token) {
+      config.headers.Authorization = `Bearer ${session.token.access_token}`;
     }
     return config;
   },