Branch Graph Plugin: Tree-based Management of Fork Sessions

The DeepSeek Harness Branch Map plugin is designed to address the management challenges of parallel multi-session workflows. It manages forked sessions through a tree-based visual graph and supports adding annotations to each branch, persistent layouts, and status filtering. Installation is simple, requiring only a single command to enable. Data is stored in a local `.branchmap` folder, with zero dependencies and no build steps, helping users efficiently track context and task branches.