feat(git): pull worktrees from origin

[markwylde]

Summary

• add a Pull from origin action to each eligible worktree context menu
• pull the selected worktree current branch from origin through the Electron bridge
• refresh Explorer and Git state after completion and surface failures in the existing error banner
• cover the Git operation against a temporary remote and the context-menu entry in Playwright

Testing

• npm run smoke
• npm run test:git-worktree-status
• npx playwright test e2e/file-explorer-sidebar.spec.ts --grep "git sidebar pane shows no changes"