DeepSeek Harness Timeline Navigator: Adding a searchable timeline for long conversations

DeepSeek Harness Timeline Navigator is a lightweight timeline navigation plugin maintained by 7A7K (MIT license), designed to solve the problem of excessive content in long conversations within DeepSeek Harness, which makes it difficult to locate key information. By utilizing the host application's `ChatSnapshot` and `data-chat-anchor-key` contracts, this plugin converts linear conversations into a browsable and searchable structured view without modifying the host source code. Its core features include message search and navigation, grouping and collapsing/expanding by turn, session bookmark management, highlighting currently visible messages, and automatically loading history when jumping to unloaded content. The plugin supports a mobile bottom panel and respects the `prefers-reduced-motion` preference.