Backfill Event Definition

Enqueue a wider-window historical backfill for one definition.

Validates the definition belongs to the caller's org (foreign/unknown id → 404) and enqueues one run_event_sync job with an explicit (start, end) pair derived from window_days. The runner is shared with the cron + manual /sync paths — backfill differs only in the window the caller passes, so the source-pull → resolve → upsert path stays single-source-of-truth.

Rate-limited 1/60s per (org, user, event_definition_id) so a user can backfill multiple distinct definitions in quick succession but can't re-fire the same one within the cooldown. The check is inline rather than decorator-form because FastAPI binds dependency-decorator rate limits before path params resolve, so a per-path-param key can't be expressed at the decorator. /sync's 2/60s remains decorator-form because it's coarser-grained.