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/partials/new_set_form.html

@@ -1,5 +1,5 @@
 <form class="w-full" id="new-set-workout-{{ workout_id }}"
-    hx-post="{{ url_for('create_topset', person_id=person_id, workout_id=workout_id) }}" hx-swap="beforeend"
+    hx-post="{{ url_for('workout.create_topset', person_id=person_id, workout_id=workout_id) }}" hx-swap="beforeend"
     hx-target="#new-workout" _="on htmx:afterOnLoad if #no-workouts add .hidden to #no-workouts end
                     on topsetAdded
                     render #notification-template with (message: 'Topset added') then append it to #notifications-container
@@ -52,7 +52,7 @@
 </form>
 
 <div hx-trigger="exerciseSelected from:body"
-    hx-get="{{ url_for('get_most_recent_topset_for_exercise', person_id=person_id, workout_id=workout_id) }}"
+    hx-get="{{ url_for('workout.get_most_recent_topset_for_exercise', person_id=person_id, workout_id=workout_id) }}"
     hx-target="#new-set-workout-{{ workout_id }}" hx-include="[name='exercise_id']">
 </div>