[Package Request]: siGit Code v1.5.7

Nobody has claimed this yet.

### How can we help?

I would like someone else to build the manifest.

### Please read and ensure the following

- [x] The installer meets the above requirements

### Please provide the following information

Download Page Url: https://github.com/getsigit/sigit/releases/download
Publisher: getSigit
Package Name: siGit Code
Description:
> siGit Code is a local coding agent. It runs on your machine, not someone
> else's. No API keys, no cloud round-trips, no subscription.
>
> It works two ways from the same binary. Zed and other ACP-compatible
> editors start it over stdio and talk the Agent Client Protocol to it. Run
> it from a terminal and you get an interactive chat UI instead. On Windows
> it speaks ACP; the full-screen terminal UI is Unix-only.
>
> Inference runs on-device against a GGUF model, or against siGit Code Cloud
> or any OpenAI-compatible endpoint you point it at.

Package Version: 1.5.7
Installer Url:
- https://github.com/getsigit/sigit/releases/download/v1.5.7/sigit-win-amd64.exe
- https://github.com/getsigit/sigit/releases/download/v1.5.7/sigit-win-arm64.exe

Start by reviewing the repository's existing package-manifest conventions, then inspect the two provided Windows installer URLs and the package details for siGit Code v1.5.7. Done means a manifest is prepared for both amd64 and arm64 installers and is ready for repository validation.

Written by the indexing model from the issue text.