Add training playground with reset capability (Priority 3 #3)

Training Playground Features:
- Interactive playground mode with prerequisite validation
- Reset capability to clear progress and state
- Progressive training that skips completed stages
- Progress tracking via .training_progress file
- Sandbox state directory for safe experimentation

New Functions:
- load_progress() - Load completed stages from progress file
- save_progress() - Save completed stages to progress file
- reset_training_state() - Clear all progress and state
- check_prerequisites() - Integrate with generate_prerequisite_checks.py
- show_playground_menu() - Interactive playground menu
- check_all_prerequisites() - Validate all stages
- playground_run_stage() - Run stage with prerequisite check
- playground_run_complete() - Progressive complete training

Updates:
- TOTAL_STAGES increased from 7 to 10 (includes stages 0, 8, 9)
- Updated training stages list in overview
- Updated show_menu() to add playground option
- Updated run_complete_training() for stages 0-9
- Updated review_progress() to load from progress file
- Updated view_logs() for stages 0, 8, 9
- Added --playground command-line option
- Added .training_progress and .training_state to .gitignore

.gitignore

@@ -48,6 +48,12 @@ data/
 apps/blockchain-node/data/
 cli/config/
 dev/cache/logs/
+
+# ===================
+# Training State
+# ===================
+scripts/training/.training_progress
+scripts/training/.training_state/
 dev/config/
 dev/test-nodes/*/data/
 # Keep coordinator-api data directory (contains application code)