Finalize macOS support

[erik-sutton95]

Finalize macOS support. Today macOS is a test host for the Swift core (Package.swift platforms include macOS 12 so swift test runs). There is no Mac app target, no Catalyst, no SUPPORTS_MACCATALYST.

Related: Data over USB · Live streaming · iPad · roadmap index

Why this is hard

• Pairing uses CoreBluetooth + NEHotspotConfiguration (iOS). Mac Wi-Fi join is a different, more hostile API
• Protocol notes: must run on a physical iPhone for the real spine
• Catalyst would still not give us Hotspot Configuration

Possible products (pick one in this thread)

1. Status quo — Mac stays swift test + future USB/relay tools. Honest README.
2. Mac viewer — decode + scopes only, fed by iPhone relay / USB / file. No camera join.
3. Native Mac operator — BLE + manual Wi-Fi join to OSMO-* + UDP 9004. Highest cost, closest to “finalize.”

Workstreams if we choose 2 or 3

• Decide viewer vs operator in this discussion before XcodeGen grows a Mac target
• Mac target in ios/project.yml or a separate macos/ shell — do not infect the iOS entitlements plist
• Menu bar rec tally / battery if we go operator
• Hotspot: document the manual join; do not fake NEHotspotConfiguration
• USB / Ethernet backhaul only after those investigational threads report

Done when

README says exactly what Mac can do (tests, viewer, or operator), and the Xcode project matches that sentence.

[erik-sutton95]

Tracked as maintainer task #99.