dsh-debt-snowball: Debt Snowball Calculator

`dsh-debt-snowball` is a DeepSeek Harness (DSH) plugin developed by uckkk, focused on debt snowball method calculations. The plugin provides a pure Node.js local implementation with no external API dependencies and can return detailed calculation results based on input parameters. Users can install it with the `dsh plugin add` command, after which the `debt_snowball` tool can be invoked in a session. It is suitable for local debt planning agents, runs with the permissions of the current DSH process, and is available under the MIT license.