Rates refresh by themselves and show when they were last updated #78

Blocked by: #70, #71

Problem

The scheduled refreshes and the "last updated" display are built separately. Nothing checks that rates actually update on their own, or that the manager can tell when they're stale.

Goal

On production, rates update by themselves after new events appear, and the app shows when each kind of data was last refreshed.

Scope

• Connect the "last updated" display to the API.
• Watch a real new event flow through to updated rates without anyone acting.

Acceptance criteria

• A new event leads to updated rates within the agreed time, with no one calling the API.
• The app shows the last successful events refresh, weather refresh, upload and training times.
• Stale data is obvious to the manager.