refactor(frontend/auth): Move /copilot auth check to middleware (#12053)

These "is the user authenticated, and should they be?" checks should not
be spread across the codebase, it's complex enough as it is. :')

- Follow-up to #12050

### Changes 🏗️

- Revert "fix(frontend): copilot redirect logout (#12050)"
- Add `/copilot` to `PROTECTED_PAGES` in `@/lib/supabase/helpers`

### Checklist 📋

#### For code changes:
- [x] I have clearly listed my changes in the PR description
- [x] I have made a test plan
- [x] I have tested my changes according to the test plan:
  - [x] Trivial change, we know this works for other pages

autogpt_platform/frontend/src/app/(platform)/copilot/useCopilotPage.ts

@@ -3,7 +3,6 @@ import { useBreakpoint } from "@/lib/hooks/useBreakpoint";
 import { useSupabase } from "@/lib/supabase/hooks/useSupabase";
 import { useChat } from "@ai-sdk/react";
 import { DefaultChatTransport } from "ai";
-import { useRouter } from "next/navigation";
 import { useEffect, useMemo, useState } from "react";
 import { useChatSession } from "./useChatSession";
 
@@ -11,7 +10,6 @@ export function useCopilotPage() {
   const { isUserLoading, isLoggedIn } = useSupabase();
   const [isDrawerOpen, setIsDrawerOpen] = useState(false);
   const [pendingMessage, setPendingMessage] = useState<string | null>(null);
-  const router = useRouter();
 
   const {
     sessionId,
@@ -54,10 +52,6 @@ export function useCopilotPage() {
     transport: transport ?? undefined,
   });
 
-  useEffect(() => {
-    if (!isUserLoading && !isLoggedIn) router.replace("/login");
-  }, [isUserLoading, isLoggedIn]);
-
   useEffect(() => {
     if (!hydratedMessages || hydratedMessages.length === 0) return;
     setMessages((prev) => {

autogpt_platform/frontend/src/lib/supabase/helpers.ts

@@ -6,6 +6,7 @@ import { SupabaseClient } from "@supabase/supabase-js";
 export const PROTECTED_PAGES = [
   "/auth/authorize",
   "/auth/integrations",
+  "/copilot",
   "/monitor",
   "/build",
   "/onboarding",