test: standardize naming conventions to snake_case

- Rename demo_event_id → testing_event_id (more explicit)
- Rename demo_account_id → testing_account_id (matches convention)
- Rename demo_badge_id → event_badge_id (descriptive)
- Rename demo_template_id → event_badge_template_id (explicit)
- Update all test files for consistency (15 files)
- Enhance README with organized test data sections
- Update person IDs to match README test data
- No regression: 15 tests passing, 7 pre-existing failures unchanged

tests/_helpers/env.ts

@@ -4,14 +4,14 @@
  */
 export const test_base_url = 'http://demo.localhost:5173';
 export const dev_api_base = 'https://dev-api.oneskyit.com';
-export const demo_account_id = '_XY7DXtc9MY';
-export const demo_event_id = 'pjrcghqwert';
+export const testing_account_id = '_XY7DXtc9MY';
+export const testing_event_id = 'pjrcghqwert';
 
 export const TEST_ENV = {
   test_base_url,
   dev_api_base,
-  demo_account_id,
-  demo_event_id
+  testing_account_id,
+  testing_event_id
 };
 
 export default TEST_ENV;