feat: Refactor workout functionality into blueprint

- Moved workout-related routes (create/delete/edit workouts, topsets, tags, start dates, show workout) from `app.py` into a new blueprint at `routes/workout.py`.
- Integrated workout view model logic from `features/workout.py` directly into `routes/workout.py` helper function `_get_workout_view_model`.
- Removed `features/workout.py` and the corresponding class instantiation in `db.py`.
- Registered the new `workout_bp` blueprint in `app.py`.
- Removed the original workout route definitions from `app.py`.
- Updated `url_for` calls in relevant templates (`workout.html`, `person_overview.html`, `partials/workout_tags.html`, `partials/topset.html`, `partials/start_date.html`, `partials/new_set_form.html`, `notes.html`, `calendar.html`) to reference the new blueprint endpoints (e.g., `workout.create_workout`).
- Updated `templates/changelog/changelog.html` to document this refactoring.

templates/workout.html

@@ -75,7 +75,7 @@
 
                 <button type="button"
                     class="absolute right-0 text-gray-400 bg-transparent hover:bg-gray-200 hover:text-gray-900 rounded-lg text-sm p-1.5 ml-auto inline-flex items-center dark:hover:bg-gray-600 dark:hover:text-white mr-2"
-                    hx-get="{{ url_for('delete_workout', person_id=person_id, workout_id=workout_id) }}"
+                    hx-get="{{ url_for('workout.delete_workout', person_id=person_id, workout_id=workout_id) }}"
                     hx-confirm="Are you sure you wish to delete this workout?" hx-push-url="true"
                     hx-target="#container">
                     <svg aria-hidden="true" class="w-5 h-5" fill="currentColor" viewBox="0 0 20 20"