dsh-achievements: Adding Cross-Session Achievements, Badges, and Agent Wrapped to DSH

dsh-achievements is an achievements and gamification plugin for DeepSeek Harness (DSH), designed to organize usage traces scattered across different sessions (such as turns, tool calls, and daily activities) into queryable and shareable achievement states. Built on DSH's philosophy of "everything is a plugin," this plugin leverages the official read-only `session/event` events for functionality without requiring modifications to the DSH core code. Core features include 68 achievements covering lifelong growth lines, session behavior badges, and trajectory achievements; support for real-time unlock push notifications via SSE; a profile card, rarity statistics, and badge wall display on the settings page; generation of privacy-safe share cards and Agent Wrapped; and an open SDK allowing third-party plugins to register custom achievements. Data is persisted.