fix: Resolve Supabase SSR cookie handling and auth test page issues

- Add null checks for cookies object in Supabase SSR client
- Fix auth test page to use Astro.cookies instead of Astro.request
- Prevent "Cannot read properties of undefined" errors in cookie handling
- Ensure proper unified auth usage pattern in test pages

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

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

src/lib/supabase-ssr.ts

@@ -12,12 +12,15 @@ export function createSupabaseServerClient(
     {
       cookies: {
         get(name: string) {
+          if (!cookies) return undefined;
           return cookies.get(name)?.value
         },
         set(name: string, value: string, options: CookieOptions) {
+          if (!cookies) return;
           cookies.set(name, value, options)
         },
         remove(name: string, options: CookieOptions) {
+          if (!cookies) return;
           cookies.delete(name, options)
         },
       },