fix(io_pool): increase worker count from 4 to 8 to prevent test hangs

Root cause: test_full_live_workflow in batch context (with prior sims
running AI discussion turns) would queue its _do_project_switch behind
the auto-pruner's scan of tests/logs/ (154MB, 6519 files). The 4-worker
pool was saturated, so the switch would never run within 30s.

Fix: bump IO_POOL_MAX_WORKERS from 4 to 8. This gives the pool enough
capacity to run: 2 pruners + the project switch + 5 spare.

Also: add /api/io_pool_status endpoint + get_io_pool_status +
wait_io_pool_idle helpers (kept in api_hooks.py and api_hook_client.py
for the test_api_hook_client_io_pool.py tests, even though the test
itself no longer uses them - they remain useful for future tests that
want to assert pool state directly).

Also: add wait_for_warmup at the start of test_full_live_workflow to
ensure SDK modules are loaded before AI ops.

Test verification:
- test_full_live_workflow in isolation: 11.83s PASS
- test_full_live_workflow in batch (with 4 prior sims): 83.46s PASS
- 30/30 related unit tests PASS

src/io_pool.py

@@ -17,7 +17,7 @@ the broken finalization chain. See commit log for details.
 from concurrent.futures import ThreadPoolExecutor
 
 
-IO_POOL_MAX_WORKERS: int = 4
+IO_POOL_MAX_WORKERS: int = 8
 IO_POOL_THREAD_NAME_PREFIX: str = "controller-io"