ci(deploy): add cloudflare deployment workflow

[Tuxedolphin]

Summary

• add a Cloudflare deploy workflow for the Vite frontend using Pages Direct Upload
• optionally deploy the /api/* Worker proxy when Worker backend/origin variables are configured
• document the required Cloudflare GitHub secrets and variables

Verification

• workflow YAML parse passed
• attribution scan for Claude/Codex/generated-by strings returned no matches
• uv run --python 3.13 ruff check backend tests
• npx --yes wrangler@latest deploy --dry-run --config deploy\cloudflare-api-proxy\wrangler.jsonc
• pnpm lint
• uv run --python 3.13 pytest tests/ (827 passed)
• pnpm test (23 passed)
• pnpm build
• pnpm audit --audit-level moderate
• git diff --check

Notes

• This deploys the frontend to Cloudflare Pages and the Worker API proxy to Cloudflare. The current symbolic backend remains a Python service configured as the Worker BACKEND_ORIGIN.