Continues #708 / #710 by growing
`tests/clickhouse-test-runner/upstream-allowlist.txt` from 36 → 424
entries through the Node.js harness, validated on both `client` and
`http` backends.

- [x] Set up upstream ClickHouse sparse checkout, install Python deps,
build the test runner, start ClickHouse via docker-compose
- [x] Verify the existing 36-test allowlist passes through the harness
on both `client` and `http` backends
- [x] Build the per-batch driver (add 100, run both backends with
`--no-stateful --no-long`, keep passers, drop failures and skips)
- [x] Run batches 1-6 (600 candidates evaluated; 342 passed on both
`client` and `http` backends and were kept; 257 failures and 1 skip
dropped); allowlist 36 → 378
- [x] Fix CI failures from prior commit: drop 54 entries from the
allowlist that either failed in the CI matrix (`{client,http} ×
{head,latest}`) or that act as **prefix matches** for failing tests
(clickhouse-test treats positional args as substring/prefix matches, so
e.g. `00396_uuid` was unintentionally pulling in the failing
`00396_uuid_v7`). Net: allowlist now 424 entries (+388 vs the pre-#710
baseline of 36)
- [x] Document the harness purpose and the batch-add strategy (including
the prefix-match gotcha) in `AGENTS.md` so future agent runs have the
context
- [x] PR ready for review

---------

Co-authored-by: copilot-swe-agent[bot] <198982749+Copilot@users.noreply.github.com>
Co-authored-by: peter-leonov-ch <209667683+peter-leonov-ch@users.noreply.github.com>