[codex] Scrape Young signup events

[tiankaima]

Summary

• Add a Young signup event scraper that logs into the SignUp app with Playwright, extracts the Young access token, then fetches event APIs through HTTP requests.
• Store active events every run and reuse cached ended events when the upstream ended total has not changed.
• Add dynamic JSON response storage so the full upstream event payload, including nested fields, is preserved in SQLite.

Validation

• uv run python -m unittest discover -s tests -p 'test_*.py'
• uv run ruff check .
• uv run python -m compileall main.py src tests
• git diff --check
• Clean local uv run python main.py --young: 17 active events, 2641 ended events, refreshed=True, SQLite PRAGMA quick_check = ok
• Incremental local uv run python main.py --young: 17 active events, 2641 ended events, refreshed=False, SQLite PRAGMA quick_check = ok