Taxicode On Demand stats.

Added an On Demand stats table to Taxicode's admin dashboard by extending the existing analytics query with a single backwards-compatible mode parameter, so every existing call site behaves exactly as before. Verified with a Docker smoke test that runs the change on the three PHP versions in Taxicode's estate.

• One new parameter with a default that keeps existing behaviour byte-identical
• Smoke tests run in Docker against PHP 5.6, 7.2 and 8.2
• Seeded MySQL schema and test doubles so it runs without production access