feat(projects): add pre-build stats fetching

[CalvinAllen]

Summary

• Add scripts/fetch-project-stats.js to fetch GitHub and marketplace stats as a pre-build step
• Stats are fetched based on project category:
  • nuget-package: GitHub + NuGet
  • vs-extension/vscode-extension: GitHub + VS Marketplace
  • cli-tool/desktop-app/documentation/github-action: GitHub only
• Update workflow to use build:with-stats with GITHUB_TOKEN for authenticated GitHub API calls
• Update projects.ts to read from cached stats JSON instead of fetching at build time
• Remove marketplace-stats.ts (replaced by pre-build script)
• Fix NuGet package URLs to use correct CodingWithCalvin. prefix
• Add npm scripts: fetch:stats, build:with-stats

Test plan

• Verify npm run fetch:stats fetches stats correctly with category-based logic
• Verify npm run build:with-stats runs fetch then build
• Verify GitHub Actions builds successfully with GITHUB_TOKEN
• Verify stats appear on project listing and detail pages