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>

templates/assessment_form.html

@@ -5,7 +5,7 @@
 {% block content %}
 <div class="max-w-2xl mx-auto">
     <div class="mb-6">
-        <a href="{{ url_for('assessments') }}" class="text-blue-600 hover:text-blue-800 text-sm font-medium">
+        <a href="{{ url_for('assessments.list') }}" class="text-blue-600 hover:text-blue-800 text-sm font-medium">
             ← Retour aux évaluations
         </a>
     </div>
@@ -91,7 +91,7 @@
             </div>
             
             <div class="flex justify-end space-x-3 pt-4 border-t border-gray-200">
-                <a href="{{ url_for('assessments') }}" class="px-4 py-2 border border-gray-300 rounded-md text-sm font-medium text-gray-700 hover:bg-gray-50 transition-colors">
+                <a href="{{ url_for('assessments.list') }}" class="px-4 py-2 border border-gray-300 rounded-md text-sm font-medium text-gray-700 hover:bg-gray-50 transition-colors">
                     Annuler
                 </a>
                 {{ form.submit(class="px-4 py-2 bg-blue-600 text-white rounded-md text-sm font-medium hover:bg-blue-700 transition-colors") }}