Preserve fork PR upstreams when preparing local and worktree threads

- add GitCore helpers to ensure remotes, fetch remote branches, and set upstreams
- extend GitHub CLI parsing to include cross-repo PR metadata and repo clone URLs
- update GitManager flow and tests to materialize fork heads and keep tracking on fork remotes
b36888e9ccJulius Marminge committed on 3/10/2026, 5:50:45 AM· committed by Julius Marmingeparent9bb9023
8 files changedLine totals unavailable