Add WinGet package manager support

[Copilot]

This PR adds comprehensive WinGet package manager support to enable Windows users to install G using Microsoft's official package manager.

What's Added

1. WinGet Manifest Generation (winget/winget.sh)

• Generates proper WinGet manifest YAML files following Microsoft's schema v1.6.0
• Supports all Windows architectures (x64, x86, arm64)
• Automatically calculates SHA256 checksums for release binaries
• Creates correct directory structure for WinGet submissions (manifests/e/Equationzhao/G/{version}/)

2. Build System Integration

• Added winget task to justfile following the same pattern as existing scoop task
• Added generated manifests to .gitignore as build artifacts

3. Documentation Updates

• README.md: Replaced "TODO" placeholder with actual installation command
• g_streamlit.py: Updated to show WinGet support instead of "In development"
• docs/ReleaseWorkflow.md: Added complete WinGet submission workflow
• winget/README.md: Comprehensive documentation for maintainers

Generated Manifest Structure

The script creates three manifest files required by WinGet:

1. Equationzhao.G.yaml - Version manifest
2. Equationzhao.G.installer.yaml - Installer manifest with download URLs and checksums
3. Equationzhao.G.locale.en-US.yaml - Package metadata with descriptions and tags

Usage

For maintainers:

just winget  # Generate manifests after building Windows binaries

For users (once submitted to winget-pkgs):

winget install Equationzhao.G

Next Steps

1. Build Windows binaries using the existing build system
2. Generate WinGet manifests using just winget
3. Submit manifests to microsoft/winget-pkgs repository

This follows the established pattern used for other package managers (Scoop, AUR, Homebrew) and provides a seamless installation experience for Windows users.

Fixes #119.

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