refact: remove exercise detail pages and modernize assessment interface

- Remove routes/exercises.py blueprint (only consultation routes)
- Delete templates/exercise_detail.html (intermediate page removed)
- Update app.py to remove exercises blueprint registration
- Modernize templates/assessment_detail.html with:
  * Hero section with gradient background
  * Action cards with hover effects and animations
  * Centered progress indicator with visual circles
  * Compact exercise structure display
  * Improved responsive design and UX

Part of Phase 2 UX improvements - eliminating intermediate pages for direct navigation.

🤖 Generated with [Claude Code](https://claude.ai/code)

Co-Authored-By: Claude <noreply@anthropic.com>

app.py

@@ -10,7 +10,6 @@ from core.logging import setup_logging
 
 # Import blueprints
 from routes.assessments import bp as assessments_bp
-from routes.exercises import bp as exercises_bp
 from routes.grading import bp as grading_bp
 from routes.config import bp as config_bp
 
@@ -40,7 +39,6 @@ def create_app(config_name=None):
 
     # Register blueprints
     app.register_blueprint(assessments_bp)
-    app.register_blueprint(exercises_bp)
     app.register_blueprint(grading_bp)
     app.register_blueprint(config_bp)