Add Session Cost Ledger to DeepSeek Harness Web Interface with dsh-cost-meter

`dsh-cost-meter` is a DeepSeek Harness community plugin maintained by Han-1413141. It counts the session cost, daily total, budget progress and official balance in the Web UI, and synchronizes prices with the official pricing page based on peak-valley pricing. This article verifies the installation command, ledger caliber and permission boundary according to the plugin directory page, GitHub README and `package.json` 1.3.1: the badges are estimates, the exact amount shall prevail based on the local ledger, and the budget only serves as a reminder without blocking.