dsh-turn-approval: Add task-level authorization for DSH Web approval cards

dsh-turn-approval is a community plugin for DeepSeek Harness (DSH) designed to address the operational costs associated with repeated approvals for high-privilege operations under default permissions. This plugin introduces an "Allow this task" button to the DSH Web approval card, enabling users to temporarily permit specific types of `danger-full-access` escalation within a single `turn`, with the authorization automatically expiring upon `turn/end`. Its core advantage lies in the balance between security and convenience: it does not alter the default permission model or enable global `full access`. Authorization is stored only in memory and bound to specific `session` and `turn` contexts; child agents do not inherit this authorization, and it only automatically allows explicitly matched `danger-full-access`.