Entire adds git-sync for remote mirroring

This is a practical, low-glamour feature that actually fits the problem space: when code and context need to move together, bare-remote syncing is more useful than another pretty agent demo.

• –Removes the need for a working tree, which makes mirroring, backup, and migration jobs cleaner and easier to automate
• –Fits Entire’s positioning as an agent-native forge by treating Git refs as transport, not just developer workflow state
• –More useful for teams with multiple remotes, repo migrations, or mirrored environments than for everyday single-remote Git users
• –The real test will be guardrails: ref selection, overwrite safety, and how well it handles partial syncs or protected branches
• –If Entire can make this reliable, it becomes part of the plumbing that keeps agent-era codebases portable