Implements both Option A and B for admin token management:
- Option A (mode='remaining'): Set tokens remaining to use (calculates usage from limit)
- Option B (mode='usage'): Directly set tokens consumed
- Original mode='limit': Still sets token limit override
The admin UI now presents 3 modes via prompt dialog, and the API endpoint
handles each mode appropriately by updating the token usage bucket.
0ce352ad8d