## Description
A single account deleted ~167,000 conversations via the API in 60
minutes (avg 46 rps, peak 151 rps/min) on 15 Jun 2026 21:00 to 22:00
IST. The cascade through `dependent: :destroy_async` on conversations,
then messages, then reporting_events, created enough job queue and DB
pressure to drive RDS CPU to ~93%, triggering 5xx alerts and
connection-pool timeouts.
This adds a `Rack::Attack` per-account throttle on `DELETE
/api/v1/accounts/:id/conversations/:id`:
- Default 60 req/min per account; configurable via the
`RATE_LIMIT_CONVERSATION_DELETE` env var.
Fixes [CW-7356](https://linear.app/chatwoot/issue/CW-7356)
