refactor: restructure codebase into modular architecture

- Split monolithic app.py (400+ lines) into organized modules
- Extract models, forms, and commands into separate files
- Implement Flask blueprints for route organization
- Maintain full functionality with cleaner architecture
- Update all templates to use new blueprint URLs
- Enhance README with technical documentation

Structure:
├── app.py (50 lines) - Flask app factory
├── models.py (62 lines) - SQLAlchemy models
├── forms.py (43 lines) - WTForms definitions
├── commands.py (74 lines) - CLI commands
└── routes/ - Blueprint modules for each feature

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

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

routes/grading.py

@@ -0,0 +1,78 @@
+from flask import Blueprint, render_template, redirect, url_for, flash, request
+from models import db, Assessment, Student, Grade, GradingElement, Exercise
+
+bp = Blueprint('grading', __name__)
+
+@bp.route('/assessments/<int:assessment_id>/grading')
+def assessment_grading(assessment_id):
+    assessment = Assessment.query.get_or_404(assessment_id)
+    students = Student.query.filter_by(class_group_id=assessment.class_group_id).order_by(Student.last_name, Student.first_name).all()
+    
+    # Get all grading elements for this assessment
+    grading_elements = []
+    for exercise in assessment.exercises:
+        for element in exercise.grading_elements:
+            grading_elements.append(element)
+    
+    # Get existing grades
+    existing_grades = {}
+    for grade in Grade.query.join(GradingElement).join(Exercise).filter_by(assessment_id=assessment_id).all():
+        key = f"{grade.student_id}_{grade.grading_element_id}"
+        existing_grades[key] = grade
+    
+    return render_template('assessment_grading.html', 
+                         assessment=assessment, 
+                         students=students, 
+                         grading_elements=grading_elements,
+                         existing_grades=existing_grades)
+
+@bp.route('/assessments/<int:assessment_id>/grading/save', methods=['POST'])
+def save_grades(assessment_id):
+    assessment = Assessment.query.get_or_404(assessment_id)
+    
+    for key, value in request.form.items():
+        if key.startswith('grade_'):
+            # Parse key: grade_<student_id>_<element_id>
+            parts = key.split('_')
+            if len(parts) == 3:
+                student_id = int(parts[1])
+                element_id = int(parts[2])
+                
+                # Find or create grade
+                grade = Grade.query.filter_by(
+                    student_id=student_id,
+                    grading_element_id=element_id
+                ).first()
+                
+                if value.strip():  # If value is not empty
+                    if not grade:
+                        grade = Grade(
+                            student_id=student_id,
+                            grading_element_id=element_id,
+                            value=value
+                        )
+                        db.session.add(grade)
+                    else:
+                        grade.value = value
+                elif grade:  # If value is empty but grade exists, delete it
+                    db.session.delete(grade)
+    
+    # Handle comments
+    for key, value in request.form.items():
+        if key.startswith('comment_'):
+            parts = key.split('_')
+            if len(parts) == 3:
+                student_id = int(parts[1])
+                element_id = int(parts[2])
+                
+                grade = Grade.query.filter_by(
+                    student_id=student_id,
+                    grading_element_id=element_id
+                ).first()
+                
+                if grade:
+                    grade.comment = value.strip() if value.strip() else None
+    
+    db.session.commit()
+    flash('Notes sauvegardées avec succès !', 'success')
+    return redirect(url_for('grading.assessment_grading', assessment_id=assessment_id))