dsh-approval-mode: Add a toggleable approval mode button to DSH

# Introduction When running agent tasks with DSH, permissions are generally selected from three tiers: Read Only, Workspace Write, and Full Access. Choosing Workspace Write restricts file operations within the sandbox to the workspace, which is safer; however, the downside is that every tool invocation requires a manual approval click. With numerous task steps, these confirmations significantly disrupt the workflow. Switching to Full Access eliminates the approval popups but also removes sandbox restrictions on file operations, keeping the two features coupled. `dsh-approval-mode` decouples these two aspects: it maintains the Workspace Write permission while adding an "Approval Mode" button nearby, transforming "step-by-step confirmation" into an independent toggle. The following introduces this plugin.