Rate limiting database schema

Table quota {
  id          uuid pk
  name        text unique not null   // api:reads, ai:generations
  window_sec  int not null
  max_count   int not null
}

Table rate_bucket {
  key            text not null   // user:123, ip:1.2.3.4
  quota_id       uuid [ref: > quota.id]
  window_started timestamptz not null
  count          int not null default 0
  pk (key, quota_id, window_started)
}

Table rate_audit {
  id         uuid pk
  key        text not null
  quota_id   uuid [ref: > quota.id]
  occurred_at timestamptz default `now()`
  denied     boolean not null
  metadata   jsonb
}