Overleaf git: collaborators push mid-session, so check before resolving conflicts

The Overleaf git bridge auto-commits a co-author's live browser edits as 'Update on Overleaf.' commits, sometimes seconds apart. So a pull/commit/push cycle can be rejected over and over while someone is typing. Pull before committing, and when a conflict involves a teammate's in-progress text, ask the user which version to keep instead of picking one. Then fetch+merge+push in one quick retry loop (e.g. merge -s ours once the user has chosen their version). The remote branch is usually 'main', not 'master'. Pass the token only in the one-off URL so it is never stored in the git config. Also, after a conflicted 'git stash pop', 'checkout --theirs' gives the upstream side, not the stash: use 'git checkout stash@{0} -- file' to get your stashed version.