feat: add admin setup page and login redirect for admins

- Add /setup-admin page for first-time admin account creation
- Add /api/admin/setup route (only works when no admin exists)
- Update login to redirect admins to /admin instead of /dashboard
- Setup page creates auth user + profile with is_admin=true

https://claude.ai/code/session_01H2aRGDaKgarPvhay2HxN6Y

app/login/page.tsx

@@ -21,7 +21,7 @@ export default function LoginPage() {
 
     try {
       const supabase = createClient();
-      const { error: authError } = await supabase.auth.signInWithPassword({
+      const { data: authData, error: authError } = await supabase.auth.signInWithPassword({
         email,
         password,
       });
@@ -35,6 +35,21 @@ export default function LoginPage() {
         return;
       }
 
+      // Vérifier si l'utilisateur est admin pour la redirection
+      if (authData.user) {
+        const { data: profile } = await supabase
+          .from("profiles")
+          .select("is_admin")
+          .eq("id", authData.user.id)
+          .single();
+
+        if (profile && (profile as { is_admin?: boolean }).is_admin) {
+          router.push("/admin");
+          router.refresh();
+          return;
+        }
+      }
+
       router.push("/dashboard");
       router.refresh();
     } catch {