[release] FlowChain Windows beginner installer

[FlowmemoryAI]

Summary

• add a root Windows beginner installer that installs/verifies Git, Node/npm, Python, Rust/Cargo, and Foundry
• have the installer clone/update FlowMemory and hand off to START_FLOWCHAIN_LOCAL.ps1
• update second-computer setup and troubleshooting docs so non-technical users start with one PowerShell command

Validation

• PowerShell parser check for INSTALL_FLOWCHAIN_WINDOWS.ps1
• powershell -NoProfile -ExecutionPolicy Bypass -File .\INSTALL_FLOWCHAIN_WINDOWS.ps1 -CheckOnly
• powershell -NoProfile -ExecutionPolicy Bypass -File .\INSTALL_FLOWCHAIN_WINDOWS.ps1 -SkipToolInstall -NoServers -SkipSmoke
• npm run flowchain:smoke
• git diff --check