Feature Request: Add Filtering (All / Active / Completed) and Todo Count

The current list displays all todos together, making it harder to focus on active tasks. Adding filtering options and task counters enhances usability and productivity.

### 🎯 Proposed Solution
- Add filter buttons: **All**, **Active**, **Completed**.
- Implement filtering client-side or via query params (e.g., `/api/todos?completed=true`).
- Display total todos and remaining active count.

### ✅ Expected Behavior
- Clicking a filter updates the displayed list.
- Counts update dynamically when todos change.
- Users can easily switch between views.

### 💻 Technical Notes
- Frontend: `App/src/components/TodoList.tsx`, possible updates to `App/src/api/*`.
- Backend: Optional support for query-based filtering.

### 🧪 Test Steps
1. Add multiple todos with mixed completion states.
2. Switch between filters → list updates accordingly.
3. Verify total and active count accuracy.