[DO NOT MERGE until freeze lifts] TT-9424: Sort aggregate batches by ID to prevent PostgreSQL deadlocks

[nerdydread]

Based on #1058, which was approved and merged prematurely as eead02ed before QA, so it had to be reverted by #1067 (e43a3b8f).

What this contains

This is a single git revert of #1067's squash commit, so it restores both changes that #1058 carried:

• The deadlock fix — all four sort.Slice(recs, ...) sites (pumps/sql_aggregate.go, pumps/graph_sql_aggregate.go, pumps/mcp_sql_aggregate.go, pumps/sql.go), giving every replica the same row-lock acquisition order and preventing the circular waits behind SQLSTATE 40P01.
• The flakey unit test fix — OmitIndexCreation: true in TestMCPSQLAggregatePump_WriteData, which stops the background CREATE INDEX CONCURRENTLY goroutine from racing the subtest's DROP TABLE cleanup.

Side benefit

master is currently red at e43a3b8f: TestMCPSQLAggregatePump_WriteData/tracks_errors fails at roughly 1 run in 3, because the revert took the OmitIndexCreation workaround out along with the production change. Merging this fixes that flakey test, since the fix rides along.

Verification

• Diff is the exact inverse of TT-9424: Revert "Sort aggregate batches by ID to prevent PostgreSQL deadlocks (#1058)" #1067: 8 files, +689/−9, recreating pumps/sql_deadlock_ordering_test.go.
• git diff eead02ed HEAD -- pumps/ is empty — byte-identical to the tree that was already reviewed and approved on TT-9424: Sort aggregate batches by ID to prevent PostgreSQL deadlocks #1058.
• Branched off current master, so it includes ac01deff (GCP IAM auth) and the two Kinesis fixes that the original TT-9424-sql-aggregate-deadlock branch predates.
• go build ./... and go test ./pumps/ -run 'TestSQL|TestMCPSQL' -count=1 pass locally.

Note for reviewers

The validate (Jira linter) check will fail while TT-9424 sits in Ready for Testing — that status is not in the linter's accepted list. It is not a required check. Required checks are Aggregated CI Status and Unit Tests & Linting.

Full background, test methodology, and the four-call-site verification are on TT-9424.