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.

db.py

@@ -10,7 +10,6 @@ from features.exercises import Exercises
 from features.people_graphs import PeopleGraphs
 from features.person_overview import PersonOverview
 from features.stats import Stats
-from features.workout import Workout
 from features.sql_explorer import SQLExplorer
 from features.dashboard import Dashboard
 from utils import get_exercise_graph_model
@@ -19,7 +18,6 @@ from utils import get_exercise_graph_model
 class DataBase():
     def __init__(self, app=None):
         self.stats = Stats(self.execute)
-        self.workout = Workout(self.execute)
         self.exercises = Exercises(self.execute)
         self.sql_explorer = SQLExplorer(self.execute)
         self.person_overview = PersonOverview(self.execute)