feat(coaching): Implement complete COACHING mode infrastructure

Add comprehensive COACHING mode system with:

Backend:
- core/coaching module with session persistence and metrics
- CoachingSessionPersistence for pause/resume sessions
- CoachingMetricsCollector with learning progress tracking
- REST API blueprint for coaching sessions management
- Execution integration with COACHING mode support

Frontend:
- CoachingPanel component with keyboard shortcuts
- Decision buttons (accept/reject/correct/manual/skip)
- Real-time stats display and correction editor
- CorrectionPacksDashboard for pack visualization
- WebSocket hooks for real-time COACHING events

Metrics & Monitoring:
- WorkflowLearningMetrics with confidence scoring
- GlobalCoachingMetrics for system-wide analytics
- AUTO mode readiness detection (85% acceptance threshold)
- Learning progress levels (OBSERVATION → COACHING → AUTO)

Tests:
- E2E tests for complete OBSERVATION → AUTO journey
- Session persistence and recovery tests
- Metrics threshold validation tests

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

visual_workflow_builder/backend/app.py

@@ -119,6 +119,13 @@ try:
 except ImportError as e:
     print(f"⚠️  Blueprint correction_packs désactivé: {e}")
 
+try:
+    from api.coaching_sessions import coaching_sessions_bp
+    app.register_blueprint(coaching_sessions_bp, url_prefix='/api/coaching-sessions')
+    print("✅ Blueprint coaching_sessions enregistré")
+except ImportError as e:
+    print(f"⚠️  Blueprint coaching_sessions désactivé: {e}")
+
 
 # Import WebSocket handlers (optional)
 try: