UIDevice.current is MainActor-isolated; replaced with a stable UUID
persisted in UserDefaults to avoid the async access.
Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>
Device auto-registers on first launch using hardcoded backend URL
and anon key (MarksAuth.swift). 90-day JWT stored in UserDefaults,
refreshed transparently. No settings fields needed — ClaudeService
is always active and non-optional throughout the app.
Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>