[codex] fix: default hk token secret name

[Pigbibi]

What changed

• changed the default LongBridge token secret name from longport_token to longport_token_hk
• updated the runtime config test to match the new default constant
• aligned the English and Chinese README docs with the HK/SG suffixed secret naming model

Why

HK token storage had already moved to suffixed secret names in Secret Manager. Keeping the old default longport_token could make HK fall back to the wrong secret when LONGPORT_SECRET_NAME was not explicitly set.

Impact

• HK defaults now resolve to longport_token_hk
• SG remains explicitly configured through LONGPORT_SECRET_NAME=longport_token_sg
• docs now match the actual secret layout

Validation

• PYTHONPATH=/Users/lisiyi/Projects/LongBridgePlatform:/Users/lisiyi/Projects/QuantPlatformKit/src:/Users/lisiyi/Projects/UsEquityStrategies/src python3 -m unittest tests.test_runtime_config_support -v
• bash tests/test_sync_cloud_run_env_workflow.sh