Register TortoiseGit as a maintained app: add winget input
(ee/maintained-apps/inputs/winget/tortoisegit.json), add app metadata to
outputs/apps.json, and create a platform-specific output with version,
installer URL, sha256, install/uninstall PowerShell scripts, and MSI
upgrade code (ee/maintained-apps/outputs/tortoisegit/windows.json). Also
add a frontend icon component and asset
(frontend/pages/SoftwarePage/components/icons/Tortoisegit.tsx and
website/assets/images/app-icon-tortoisegit-60x60@2x.png) and wire it
into the icons index mapping.
