dsh-usage-footer: DSH Web Usage and Cost Monitoring Plugin

`dsh-usage-footer` is a DSH Web UI plugin designed to address delays in official billing queries. It provides real-time monitoring of account balance, peak/off-peak periods, and token usage via a floating button in the bottom-right corner. The panel displays the current session’s usage, compares local ledger entries with official data, and supports light/dark themes. It is maintained by 1514100951, released under the MIT license, requires an API key configuration, and offers flexible local statistics and official data verification.