Add screenshot capture settings for token and payload optimization

[antiartificial]

Summary

• Primary screen only toggle skips secondary monitors, saving ~1,300+ tokens per extra display
• Active window only toggle captures just the frontmost window instead of the full screen, reducing noise and tokens
• JPEG quality slider (30%-100%) lets users trade image quality for smaller upload payloads

All three settings live in a new "SCREENSHOT" section in the menu bar panel, persist via UserDefaults, and are wired into both the voice response and onboarding demo capture pipelines. Defaults match existing behavior (all screens, full screen, 80% quality) so nothing changes unless a user opts in.

Files changed

• CompanionManager.swift three new @Published settings with UserDefaults persistence
• CompanionScreenCaptureUtility.swift captureAllScreensAsJPEG() accepts new parameters for filtering screens, capturing active window via SCContentFilter(desktopIndependentWindow:), and configurable JPEG compression
• CompanionPanelView.swift new "SCREENSHOT" settings section with two toggles and a slider
• ScreenshotSettingsTests.swift 17 unit tests covering defaults, persistence, struct fields, and quality boundaries

Test plan

• Verify the three new controls appear in the menu bar panel after onboarding
• Toggle "Primary screen only" on a multi-monitor setup — only cursor screen should be captured
• Toggle "Active window only" — screenshot should contain only the frontmost app window
• Adjust JPEG quality slider — verify the printed payload size in console changes accordingly
• Verify all settings survive app restart
• Run unit tests (Cmd+U)