Fix: Auto-trigger auth modal in HF Spaces

🐛 Problem Fixed:
- Users could access the app without authentication in HF Spaces
- Auth modal was not automatically shown to new users
- App was working in 'anonymous' mode instead of requiring login

🔧 Solution:
- Added automatic auth modal trigger in HF Spaces environment
- Check if user is authenticated on app startup
- Show auth modal immediately if not authenticated in HF Spaces
- Maintain no-auth behavior for local development

💡 How it works:
1. App loads in HF Spaces
2. AuthContext checks for existing authentication
3. If no auth found AND in HF Spaces → show auth modal
4. If in local dev → continue without auth

Now users will see the auth modal immediately when visiting
the HF Spaces deployment, ensuring proper authentication flow.

frontend/src/context/AuthContext.tsx

@@ -90,9 +90,10 @@ function convertHFOAuthResult(hfResult: HFOAuthResult): OAuthResult {
   const userInfo = hfResult.userInfo as any; // Type assertion for flexibility
   return {
     accessToken: hfResult.accessToken,
-    accessTokenExpiresAt: hfResult.accessTokenExpiresAt instanceof Date 
-      ? hfResult.accessTokenExpiresAt.toISOString()
-      : hfResult.accessTokenExpiresAt,
+    accessTokenExpiresAt:
+      hfResult.accessTokenExpiresAt instanceof Date
+        ? hfResult.accessTokenExpiresAt.toISOString()
+        : hfResult.accessTokenExpiresAt,
     userInfo: {
       id: userInfo.sub || userInfo.id || "unknown",
       name: userInfo.name || userInfo.preferred_username || "Unknown User",
@@ -147,7 +148,16 @@ export function AuthProvider({ children }: { children: ReactNode }) {
         localStorage.setItem(STORAGE_KEY, JSON.stringify(normalizedResult));
         dispatch({ type: "AUTH_SUCCESS", payload: normalizedResult });
       } else {
-        dispatch({ type: "SET_LOADING", payload: false });
+        // No OAuth redirect found, check if we need to show auth modal
+        const isHFSpaces = window.huggingface && window.huggingface.variables;
+        if (isHFSpaces) {
+          // In HF Spaces, we require authentication - show the modal
+          dispatch({ type: "SET_LOADING", payload: false });
+          openModal("auth-login", "Sign in to AgentGraph");
+        } else {
+          // In local development, no auth required
+          dispatch({ type: "SET_LOADING", payload: false });
+        }
       }
     } catch (error) {
       console.error("Auth check failed:", error);