dsh-better-plan-reviewer: Retrofitting DSH's Plan Review and Execution Workflow

`dsh-better-plan-reviewer` is a DSH client plugin designed to optimize the plan review process. It converts the original bottom review interface into a centered floating dialog, allowing users to specify the model and reasoning effort before execution, and supports stashing plans in the `.dsh/plans/` directory. The plugin automatically takes over the `plan-review` intent; upon confirmation, it first switches to the selected model and then approves the plan, ensuring that the plan runs under the new model. It depends on the DSH `next` channel and the `web` profile, and requires a restart and a browser refresh after installation.