api-monitor: A Resident API Usage Monitoring Plugin

`api-monitor` is a multi-provider API monitoring plugin for the DSH ecosystem. It aggregates and displays the balance, quota, and token usage of DeepSeek, GLM, OpenCode Go, and Volcengine, and supports peak/off-peak pricing as well as session data bucketing. The plugin is open-sourced under the MIT License, has no third-party dependencies, and provides a sidebar entry and a floating window to view details. Users need to install it manually; after configuring Volcengine AK/SK, they can force a data refresh via the API or view session snapshots.