Feat: Scratch MCP tool calling support. (#8263)

### What problem does this PR solve?

This is a cherry-pick from #7781 as requested.

### Type of change

- [x] New Feature (non-breaking change which adds functionality)

Co-authored-by: Kevin Hu <kevinhu.sh@gmail.com>

Dockerfile

@@ -200,6 +200,7 @@ COPY graphrag graphrag
 COPY agentic_reasoning agentic_reasoning
 COPY pyproject.toml uv.lock ./
 COPY mcp mcp
+COPY mcp_client mcp_client
 COPY plugin plugin
 
 COPY docker/service_conf.yaml.template ./conf/service_conf.yaml.template