Use shared runtime logs bucket

[Pigbibi]

Summary

• update HK snapshot artifact workflow default to the neutral shared runtime logs bucket
• update HK runtime docs to reference the migrated shared bucket paths

Verification

• migrated gs://qsl-runtime-logs-interactivebrokersquant to gs://qsl-runtime-logs-shared
• verified object counts match: total 2486, execution reports 2141, strategy artifacts 345
• verified GitHub environment variables no longer reference the old bucket
• git diff --check