## Summary
The batches list page orders by `createdAt DESC, id DESC` filtered by
environment and a created-at window, but the only supporting index on
`BatchTaskRun` was `(runtimeEnvironmentId, id)`. That index can't
satisfy the `createdAt` ordering, so on environments with a large number
of batches the query fell back to a full table scan and in-memory sort,
which could run long enough to hit the statement timeout.
## Fix
Adds `(runtimeEnvironmentId, createdAt DESC, id DESC)` on
`BatchTaskRun`. The query now reads straight from the index in order
with no sort step, returning a page with only a handful of heap fetches
instead of scanning the whole environment slice.
The migration uses `CREATE INDEX CONCURRENTLY IF NOT EXISTS`, so it
takes no table lock and is a no-op if the index already exists.
Eric Allam
9c85e0ecdc