Build Token Refresh Service

**Description:**  
Automatically refresh expired music provider tokens using refresh tokens.

**Requirements:**  
- Background service (or cron job) to:
  - Check for tokens nearing expiry
  - Use refresh token to request new access token
  - Update stored access token in DB

**Acceptance Criteria:**  
- Token refresh runs correctly
- New token used in API calls
- Logs or metrics confirm update