[fix] align workbench control-plane port

[FlowmemoryAI]

Summary

• align START_FLOWCHAIN_LOCAL.ps1, docs, installer output, and control-plane default with dashboard workbench port 8787
• simplify startup to npm run control-plane:serve so npm does not strip nested --host/--port arguments
• keep the local API health endpoint matching the workbench probe at http://127.0.0.1:8787/health

Validation

• PowerShell parser checks for START_FLOWCHAIN_LOCAL.ps1 and INSTALL_FLOWCHAIN_WINDOWS.ps1
• npm test --prefix services/control-plane
• temporary local server health probe at http://127.0.0.1:8787/health
• git diff --check