Honor precheck dry-run for order execution

[Pigbibi]

Summary

• thread dry_run_only_override into broker/order execution wiring
• make /precheck order execution use the dry-run broker adapter instead of global live runtime settings
• add a request-handling test that exercises the composer-to-order-execution path

Tests

• PYTHONPATH=. PYTEST_DISABLE_PLUGIN_AUTOLOAD=1 /tmp/ues-test-venv/bin/python -m pytest -q tests/test_request_handling.py::test_precheck_composer_wires_dry_run_override_to_order_execution tests/test_request_handling.py::test_handle_precheck_post_uses_dry_run_override tests/test_runtime_strategy_adapters.py
• ruff check main.py tests/test_request_handling.py

Note

A manual u1599 /precheck before this fix used live order execution because the override stopped at the composer/reporting layer. This patch prevents that class of precheck from submitting broker orders.