ci: the 91-test vitest suite never runs in CI; add scheduled data-freshness checks

[shauryagangrade]

Problem

• .github/workflows/ci.yml runs only data validation + build
• .github/workflows/lint.yml runs lint + tsc
• npm run test:unit (91 passing tests!) runs nowhere in CI

So unit tests can rot silently. Also missing: any schedule: trigger to re-validate place data or flag stale valid_till/exam dates (see the stale exam-dates issue), and e2e coverage for map/auth flows (#38 deferred Playwright).

Suggested fix

1. Add a test job (or extend lint.yml) running npm run test:unit on PRs
2. Add a weekly scheduled workflow that runs validation + a freshness check and opens/updates an issue on failure
3. (Follow-up) Playwright smoke: map loads, pin popup opens, login flow with stubbed Supabase

Acceptance criteria

• Unit tests gate PRs
• Scheduled job catches stale/broken data