Salvaged from PR #1116 by halfprice06.
Resolve the current branch's configured upstream before fetching
and pulling during `hermes update`. Branches tracking a non-origin
remote (e.g. fork-backed PR branches) now fetch from the correct
remote instead of unconditionally using origin.
- Add _get_update_target() to resolve upstream via git @{u}
- Fall back to origin/<branch> when no upstream is configured
- Preserve existing verify-and-fallback-to-main safety net
- Re-fetch from origin when falling back to origin/main
- 5 unit tests for the upstream resolution logic
halfprice06
02e0ee3cd0