fix(gateway): isolate Hermes memory by user

[YOMXXX]

Summary

• Scope Gateway TdaiCore instances and data directories by user_id for Hermes requests
• Keep empty/default/default_user on the legacy baseDir for backward compatibility
• Propagate user_id through Hermes search/seed client APIs and memory tool calls
• Add Gateway regression tests for persona and L0 capture isolation

Verification

• npm test -- --run
• npm run build:plugin
• python3 -m compileall -q hermes-plugin/memory/memory_tencentdb
• npx vitest run src/gateway --run

Note: npm run test:cc-plugin -- --run is not available in this package.json (Missing script: test:cc-plugin).

[Maxwell-Code07]

Thanks for the contribution! The PR is well-structured and the code quality is solid 👍

Regarding user-based memory isolation — multi-user management will be handled internally as part of our upcoming roadmap with a unified solution. That said, your implementation is well-thought-out, and we'll take some of the ideas and patterns from it as a reference for our internal work.

Appreciate your understanding and continued contributions! 🎉