Reuse existing Nemotron installs and terminate model processes

[vokac-nri]

Summary

• avoid the benign uv user-profile Python shim collision by installing the private runtime with --no-bin
• store new Nemotron installs in a stable per-user LocalAppData root shared by development and packaged builds
• discover and reuse complete legacy checkout installs instead of downloading/copying the multi-GB model again
• run provisioning in a separate visible progress window that users can close to cancel, while retaining resumable partial downloads
• reuse an existing Hugging Face login and enable Xet high-performance transfers
• explicitly exclude generated Nemotron runtime/model/cache assets from local installer payloads
• supervise local STT servers with a Windows kill-on-close Job Object and kill the full Parley process tree during upgrades

Validation

• go test ./...
• wails3 build
• PowerShell parser validation for both provisioning scripts
• reuse smoke test against the existing checkout installation (no network/download)
• cancellable provisioning wrapper smoke test
• GitHub Go, frontend, and Windows installer jobs pass
• package lock and unrelated generated binding changes remain unstaged