🏷️ Fix inconsistent testID vs testId property naming

[anbanm]

Problem

The code uses both testID and testId inconsistently, which may cause integration issues with Unity.

Current Behavior

• Line 431: Uses testID in JSON output
• Line 456: Uses testID in filename generation
• Other places use testId (lines 179, 286, etc.)

Expected Behavior

• Consistent naming throughout codebase
• Maintain compatibility with Unity integration

Files Affected

• src/frontend/quizGenerator.html
• src/unity/SampleWebView.cs

Priority

High - may break Unity integration