jaahd tests leave a detached provision accounts

A combined jaahd run leaks a detached `provision_accounts.py --config-dir <tmp>/jaah/auth/acct-… --offline` process, and the orphan-process guard fails the run with "process(es) started by this test run are STILL ALIVE". Reproduced on plain origin/develop (2026-10-18): `cd apps/jaahd && python3 -m pytest -q -p no:cacheprovider tests/test_fleet_dispatch.py tests/test_microvm_session.py tests/test_agent_adapters.py tests/test_codex_adapter.py tests/test_gemini_adapter.py tests/test_bedrock_launch.py tests/test_slot_intent_executors.py`. The two files `test_microvm_session.py` and `test_slot_intent_executors.py` run alone are clean. The leak comes from `test_microvm_session.py::test_a_linked_cli_s_credential…` reaching a provider adapter's `prepare`, which spawns `provision_accounts.detached_command(...)` (see `apps/jaahd/agents/codex.py` around the converge cooldown). Make that test, or a shared fixture, stub the detached converge so no test spawns it. Out of scope: changing the converge itself or the orphan guard. Done means: - The command above passes with no orphan-process failure, run three times in a row.

Fixed the orphaned detached converge: a conftest autouse fixture resets adapter singletons each case (an instance monkeypatch leaked and shadowed class stubs). Done-means command green 3×. Full gate: 2 reds already on develop (filed #7323). PR #5930 merged; deploy succeeded.