dsh-goal-board: Cross-session goal list plugin

dsh-goal-board is a DSH plugin maintained by Little-Mostima. It organizes goals into a three-layer structure: Project -> Goal -> Entry. It is injected into the agent every round. Goal claiming includes a heartbeat (auto-released after 30 minutes, adjustable via `DSH_GOAL_BOARD_TTL_MS`). Upon completion, the agent verifies the output before archiving. Data is stored in `.dsh/goal-board/data.json` and persists after uninstallation. The installation command is `dsh plugin add github:Little-Mostima/dsh-goal-board`. After installation, the desktop client requires a restart; the server and panel do not support hot reloading. It supports smoke testing, session activity logging, and tombstone protection. License: MIT, Version: 0.2.0.