GIT tab - improvements (branches, update/pull/rebase)

[simion]

• show current branch
• checkout a different branch (fork-style, with stash and re-apply)\

Request from coworker

[simion]

Done in v0.23.1. The Git tab shows the current branch and switches branches fork-style (stash, checkout, re-apply), and Update pulls from upstream or merges/rebases the task's base branch. GitPanel.tsx, via task_git_checkout / task_git_update.