fix: Remove client-side auth redirects causing dashboard flashing

- Removed checkAuth() function and redirects from dashboard.astro
- Removed checkAuth() function and redirects from events/new.astro
- Updated to use Astro.cookies for better SSR compatibility
- Client-side code now focuses on data loading, not authentication
- Server-side unified auth system handles all protection

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

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

src/pages/events/new.astro

@@ -7,7 +7,7 @@ import { verifyAuth } from '../../lib/auth';
 export const prerender = false;
 
 // Server-side authentication check
-const auth = await verifyAuth(Astro.request);
+const auth = await verifyAuth(Astro.cookies);
 if (!auth) {
   return Astro.redirect('/login');
 }
@@ -322,11 +322,12 @@ if (!auth) {
   // let selectedAddons: any[] = []; // TODO: Implement addons functionality
   let eventImageUrl: string | null = null;
 
-  // Check authentication
-  async function checkAuth() {
-    const { data: { session } } = await supabase.auth.getSession();
-    if (!session) {
-      window.location.href = '/';
+  // Load user data (auth already verified server-side)
+  async function loadUserData() {
+    const { data: { user: authUser } } = await supabase.auth.getUser();
+    
+    if (!authUser) {
+      console.error('No user found despite server-side auth');
       return null;
     }
 
@@ -334,14 +335,14 @@ if (!auth) {
     const { data: user } = await supabase
       .from('users')
       .select('name, email, organization_id, role')
-      .eq('id', session.user.id)
+      .eq('id', authUser.id)
       .single();
 
     if (user) {
       currentOrganizationId = user.organization_id;
     }
 
-    return session;
+    return authUser;
   }
 
   // Generate slug from title
@@ -552,9 +553,9 @@ if (!auth) {
     }
   }
 
-  // Initialize
-  checkAuth().then(session => {
-    if (session && currentOrganizationId) {
+  // Initialize (auth already verified server-side)
+  loadUserData().then(user => {
+    if (user && currentOrganizationId) {
       loadVenues();
     }
     handleVenueOptionChange(); // Set initial state