feat: implement git repository management

- Add backend API for git repository CRUD (create, list, delete)
- Support bare repository initialization and mirror cloning
- Add cascade delete for repositories when project is deleted
- Add frontend page for repository management per project
- Update project page with link to repositories
- Add repo_base_path to config
- Quality gates: ruff, mypy, typecheck, lint, build all pass

apps/web/src/components/app-shell.tsx

@@ -5,7 +5,6 @@ import { useAuth } from "../state/auth";
 const NAV_ITEMS = [
   { to: "/", label: "Dashboard" },
   { to: "/projects", label: "Projects" },
-  { to: "/repositories", label: "Repositories" },
   { to: "/ssh-keys", label: "SSH Keys" },
   { to: "/settings", label: "Settings" }
 ];