dsh-multi-root-changes: Consolidate Git changes from multiple repositories into a single panel

The plugin adds a "Multi-root Changes" tab to the DeepSeek Harness sidebar, covering the main session working directory and all registered additional roots of multi-root-workspace: it groups by root to display git status (branch, ahead/behind, added/removed lines, file counts), line-level unified diffs, split-pane previews, directory tree collapse and rename, conflict red highlighting, and binary file hints. Each root allows expanding the last 30 commit history and viewing the patch. The commit box executes `git add -- <files>` + `git commit -- <files>` for files listed in each directory (without `git add -A`) and provides AI-generated commit messages (read-only, text-delta only). The main root follows the session via `sessionId` as parsed by the host and stops polling when the tab is invisible. If `rev-parse` differs from the registered path, it is marked as belonging to another repository, with separate handling for solid background color and the theme plugin's transparent background conflict. The plugin requires both `dsh-better-sidebar` and `multi-root-workspace` to be present; otherwise, it degrades to showing only the main directory. Install using `dsh plugin --profile desktop add /path/to/dsh-multi-root-changes`; a full restart is required after installation. Known limitations are detailed in the README: no staging area operations, no commit graph, merge commits do not display patches, and there are resource and entry limits.