Usage signals page now shows real data

The usage signals page is now connected to a live API, replacing the previous mock data. The API validates date and limit parameters and returns clear errors on bad input.

The signals page now reads from a real endpoint backed by persistent signal records, so the data you see reflects your actual usage history.

Refreshing the page no longer shows stale signal data from a previous load

The signals API rejects malformed `date` and `limit` parameters with a descriptive error instead of silently failing

AI agents calling `GET /api/usage/signals` can rely on validated, structured responses