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>

stores/authStore.ts

@@ -6,6 +6,7 @@ interface AuthState {
   user: User | null;
   isAuthenticated: boolean;
   isLoading: boolean;
+  isHydrated: boolean;
 
   setUser: (user: User) => void;
   clearUser: () => void;
@@ -18,6 +19,7 @@ export const useAuthStore = create<AuthState>()(
       user: null,
       isAuthenticated: false,
       isLoading: true,
+      isHydrated: false,
 
       setUser: (user) =>
         set({ user, isAuthenticated: true, isLoading: false }),
@@ -31,6 +33,16 @@ export const useAuthStore = create<AuthState>()(
         user: state.user,
         isAuthenticated: state.isAuthenticated,
       }),
+      onRehydrateStorage: () => (state) => {
+        console.log('[AuthStore] Hydration started');
+        if (state) {
+          state.isHydrated = true;
+          console.log('[AuthStore] Hydration completed', {
+            user: state.user?.id,
+            isAuthenticated: state.isAuthenticated
+          });
+        }
+      },
     }
   )
 );