M7: Local clone (Download Repository)

[michaeljolley]

Part of the RayCast parity roadmap. Stacked on top of #293 (M6).

What this adds

Clone a GitHub repository to the local machine, respecting a configurable clone location and git availability.

• Git detection + clone: \IGitService\ / \GitService\ locate \git\ on the PATH and shell out to \git clone . Abstracted behind an interface so the clone flow is unit tested without a real git install or spawned process. MSIX sandbox constraints surface as clone failures turned into error toasts.
• Configurable clone path: \ICloneSettingsStore\ / \CloneSettingsStore\ persist the clone base directory via \LocalSettings, defaulting to %USERPROFILE%\source\repos.
• Clone orchestration: \IRepositoryCloneManager\ / \RepositoryCloneManager\ resolve the clone URL (owner/repo, GitHub URL, or clone URL) and destination directory, validate git availability, guard against a non-empty destination, and return the local clone path.
• Top-level Clone Repository command: a \FormContent\ form with a repository field and an optional target directory (placeholder shows the default).
• Per-item Clone action: a Clone Repository action on the Repositories search page items, cloning from the repo's clone URL.

Tests

• URL / owner-repo resolution, git-missing guard, configured vs explicit target directory, default-directory resolution, and form JSON rendering.
• 209/209 tests pass.

Notes

• \RuntimeHelper.IsMSIX\ currently returns false; the default clone directory stays inside the user profile so it works in both packaged and unpackaged runs.
• Repo/branch entry is text-input based, consistent with the other create/trigger forms.