- Add `require_write_api!` guard to PointsController for create, update,
destroy, and bulk_destroy actions. Lite users receive 403 with clear
JSON error and upgrade URL.
- Add `scoped_points` helper to ApiController that filters Lite users to
a 12-month timestamp window. Pro and self-hoster users see all data.
- Add rack-attack gem with Redis backend for per-plan rate limiting:
Lite 200 req/hr, Pro 1,000 req/hr, self-hosters exempt.
- Add X-RateLimit-Limit, X-RateLimit-Remaining, X-RateLimit-Reset
headers on all API responses for rate-limited plans.
- Custom 429 response with Retry-After header and upgrade URL.
- Full test coverage: 14 new specs (points write gating, read scoping,
rate limit headers, throttle behavior).