Sync LongBridge order sizing env vars

[Pigbibi]

Summary

• sync LongBridge fractional sizing environment variables into HK/SG Cloud Run services
• document the GitHub Environment variables used for dry-run and sizing overrides
• extend the workflow wiring test for the new variables

Tests

• bash tests/test_sync_cloud_run_env_workflow.sh
• /home/ubuntu/Projects/LongBridgePlatform/.venv/bin/python -m pytest tests/test_runtime_config_support.py::RuntimeConfigSupportTests::test_order_quantity_step_can_be_forced_to_whole_shares tests/test_runtime_config_support.py::RuntimeConfigSupportTests::test_fractional_quantity_step_must_be_enabled_explicitly tests/test_rebalance_service.py::RebalanceServiceNotificationTests::test_fractional_quantity_step_allows_small_soxx_target_buy tests/test_rebalance_service.py::RebalanceServiceNotificationTests::test_fractional_buy_uses_budget_when_broker_estimate_is_whole_share_zero tests/test_rebalance_service.py::RebalanceServiceNotificationTests::test_dry_run_replaces_real_order_submission_with_summary_lines