fix(frontend): Fix Zustand authStore hydration timing issue

Fix race condition where Epic form checked user authentication before
Zustand persist middleware completed hydration from localStorage.

Root cause:
- authStore uses persist middleware to restore from localStorage
- Hydration is asynchronous
- Epic form checked user state before hydration completed
- Result: "User not authenticated" error on page refresh

Changes:
- Add isHydrated state to authStore interface
- Add onRehydrateStorage callback to track hydration completion
- Update epic-form to check isHydrated before checking user
- Disable submit button until hydration completes
- Show "Loading..." button text during hydration
- Improve error messages for better UX
- Add console logging to track hydration process

Testing:
- Page refresh should now wait for hydration
- Epic form correctly identifies logged-in users
- Submit button disabled until auth state ready
- Clear user feedback during loading state

Fixes: Epic creation "User not authenticated" error on refresh

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

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

components/epics/epic-form.tsx

@@ -59,6 +59,7 @@ export function EpicForm({ projectId, epic, onSuccess, onCancel }: EpicFormProps
   const createEpic = useCreateEpic();
   const updateEpic = useUpdateEpic();
   const user = useAuthStore((state) => state.user);
+  const isHydrated = useAuthStore((state) => state.isHydrated);
 
   const form = useForm<EpicFormValues>({
     resolver: zodResolver(epicSchema),
@@ -71,12 +72,19 @@ export function EpicForm({ projectId, epic, onSuccess, onCancel }: EpicFormProps
   });
 
   async function onSubmit(data: EpicFormValues) {
-    console.log('[EpicForm] onSubmit triggered', { data, user: user?.id, projectId });
+    console.log('[EpicForm] onSubmit triggered', { data, user: user?.id, projectId, isHydrated });
 
     try {
+      // Check if auth store has completed hydration
+      if (!isHydrated) {
+        console.warn('[EpicForm] Auth store not hydrated yet, waiting...');
+        toast.error('Loading user information, please try again in a moment');
+        return;
+      }
+
       if (!user?.id) {
         console.error('[EpicForm] User not authenticated');
-        toast.error('User not authenticated');
+        toast.error('Please log in to create an epic');
         return;
       }
 
@@ -239,9 +247,9 @@ export function EpicForm({ projectId, epic, onSuccess, onCancel }: EpicFormProps
               Cancel
             </Button>
           )}
-          <Button type="submit" disabled={isLoading}>
+          <Button type="submit" disabled={isLoading || !isHydrated}>
             {isLoading && <Loader2 className="mr-2 h-4 w-4 animate-spin" />}
-            {isEditing ? 'Update Epic' : 'Create Epic'}
+            {!isHydrated ? 'Loading...' : isEditing ? 'Update Epic' : 'Create Epic'}
           </Button>
         </div>
       </form>