Adding an API route

Activates for work in services/api. Follow these steps in order.

1. Write the handler in the matching module (tickets.py for ticket routes, a new module for a new noun). Signature is (request: dict) -> dict.
2. Validate inputs first. Missing/!bad input raises ValidationError — never return an error dict by hand.
3. Do no business logic here. Call a repo (packages/db) or another service. The handler only orchestrates and shapes the response.
4. Register the route in routes.py inside build_app() — app.route("METHOD /path", handler). A route not registered there does not exist.
5. Add a test in tests/ that builds the app and dispatches the route.

Full checklist with a worked example: references/route-checklist.md.