feat(ganet): add optional device connection entrypoints

[nianyucatfish]

Summary

• add optional /user entrypoints across supported GA frontends
• keep the core installation free of GAnet dependencies; expose device dependencies through the optional device extra
• add a Windows device-connection setup SOP, including a PyPI mirror fallback for download timeouts

Validation

• git diff --check upstream/main...HEAD
• verified a three-way merge simulation against current upstream/main has no conflicts

Scope

• device interconnection remains optional; no device plugin, sidecar, credentials, pairing material, or private terminal capability is included