feat: add native macOS CoreWLAN Wi-Fi source

[AIflow-Labs]

Summary

This finishes the native macOS path discussed in #56 and ADR-025.

It adds a real CoreWLAN-backed Wi-Fi source for sensing-server --source wifi on macOS instead of falling back silently.

What changed

• add the canonical Swift helper at tools/macos-wifi-scan/main.swift
• add a reproducible helper build script and helper discovery via RUVIEW_MAC_WIFI_HELPER
• implement a typed macOS scanner in wifi-densepose-wifiscan
• wire macOS probing, auto-detection, and the native Wi-Fi task in sensing-server
• document the macOS path honestly as RSSI/scan-based sensing for presence/coarse motion, not CSI parity

Notes

• no compiled helper binaries are committed
• native macOS observations are labeled wifi:<ssid> when available, otherwise wifi:macos
• explicit --source wifi now returns a clear macOS-specific error when the helper/Wi-Fi path is unavailable instead of silently simulating

Verification

• cargo test --workspace
• cargo test --workspace --no-default-features
• cargo test -p wifi-densepose-wifiscan -p wifi-densepose-sensing-server
• ./scripts/build-mac-wifi.sh
• rust-port/wifi-densepose-rs/target/tools/macos-wifi-scan/macos-wifi-scan --probe
• rust-port/wifi-densepose-rs/target/tools/macos-wifi-scan/macos-wifi-scan --scan-once
• manual macOS run of cargo run -p wifi-densepose-sensing-server -- --source wifi ...
• API smoke check returned live wifi:macos data with non-zero BSSID observations on macOS

Addresses #56.