Add Git repository sync backend

[landeqiming666]

Short description of what this resolves:

Adds a Git repository backend for Settings Sync while preserving the existing GitHub Gist workflow.

Changes proposed in this pull request:

• Add an isolated Git sync service that initializes the User folder, commits settings, and pushes or forcefully downloads a selected branch.
• Add settings-page configuration for the sync backend, remote URL, and branch/profile, with local metadata excluded from commits.
• Add local bare-repository integration tests covering upload, unchanged uploads, forced download, ignored metadata, and invalid branches.

The remote URL can point to GitHub, GitLab, an enterprise host, or a local repository. Authentication is delegated to the installed Git client. Automatic repository creation through provider APIs is not included in this first implementation.

Fixes: #413

How Has This Been Tested?

• npm run vscode:prepublish
• ./node_modules/.bin/tsc -p ./
• ./node_modules/.bin/mocha out/test/service/gitSyncService/gitSyncService.test.js (4 passing)
• git diff --check

The repository's full legacy Mocha bootstrap still requires a runtime vscode module that is unavailable from its deprecated test package; the new Git integration suite runs independently against real local repositories.

Screenshots (if appropriate):

Not included. The change adds three fields to the existing Sync Settings page and does not introduce a new screen.

Checklist:

• I have read the contribution guidelines.
• My change requires a change to the documentation and GitHub Wiki.
• I have updated the documentation and Wiki accordingly.

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IssueHunt Summary

Referenced issues

This pull request has been submitted to:

• #413: Suggestion: Allow upload to repository

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