Fix KeyError: 'title' in stage_runner.py

- Use .get() with default value instead of direct dictionary access
- Default title: 'Stage {stage_number}'
- Fixes Stage 10 and other JSON stages without 'title' field
- Tested: Stage 10 now loads successfully

aitbc/training_setup/stage_runner.py

@@ -83,7 +83,7 @@ class StageRunner:
         
         return StageDefinition(
             stage=data['stage'],
-            title=data['title'],
+            title=data.get('title', f"Stage {data['stage']}"),
             commands=commands,
             expected=expected,
             prerequisites=data.get('prerequisites')