docs: clarify macOS live sensing setup

[Safrolomancer]

Summary

This PR clarifies the currently working macOS live Wi-Fi sensing flow and improves the UI fallback path for the legacy Python/WebSocket server.

Changes

• document the tested macOS CoreWLAN live-sensing workflow in the user guide
• add a README note that the main Rust auto-detect path still falls back to simulation on macOS
• teach the UI sensing service to fall back from same-origin /ws/sensing to ws://localhost:8765/ws/sensing for the legacy macOS/Python path
• ignore named local virtual environments such as .venv-macos-sensing

Validation

• verified live CoreWLAN helper output locally on macOS
• started the legacy python -m v1.src.sensing.ws_server path successfully
• confirmed WebSocket frames were received from the macos_wifi source
• ran node --check ui/services/sensing.service.js

[ruvnet]

Closing — the doc additions point at python -m v1.src.sensing.ws_server and python v1/data/proof/verify.py, both of which moved to archive/v1/ (PR #590 + ADR-028 archive). Re-applying this PR cleanly would mean updating those paths and verifying the legacy CoreWLAN/WebSocket entry point still works under archive/v1/src/sensing/. The intent (clarify macOS live-sensing setup) is genuinely useful — if you want to re-submit against the archive/v1 paths, happy to review.