ci(deploy): use cloudflare git integration

[Tuxedolphin]

Summary

• remove the GitHub Actions direct-upload Cloudflare deploy workflow
• document Cloudflare Pages Git integration settings for the Vite frontend
• clarify that the optional Worker proxy is deployed separately when /api/* should stay on the Pages origin

Notes

• Cloudflare's GitHub repository connection is completed in the Cloudflare dashboard via Workers & Pages -> Create application -> Pages -> Connect to Git.
• Do not create the Pages project with Wrangler Direct Upload for this app if Git integration is desired; Cloudflare Pages project modes cannot be switched later.
• No GitHub Cloudflare secrets or variables are required for the frontend Pages Git integration path.

Verification

• uv run --python 3.13 pytest tests/
• uv run --python 3.13 ruff check backend tests
• pnpm lint
• pnpm test
• pnpm build
• pnpm audit --audit-level moderate
• npx --yes wrangler@latest deploy --dry-run --config deploy\cloudflare-api-proxy\wrangler.jsonc
• git diff --check
• attribution/secrets scan across .github, README.md, deploy, frontend, backend, tests