feat: desktop/web UX alignment, window lifecycle sync, responsive layouts & layout audit tests

[spelech]

Summary

This PR addresses UI/UX divergence between Desktop and Web, fixes companion window lifecycle synchronization, introduces a responsive collapsible telemetry ribbon, resolves chat and documentation layout crowding, and adds automated layout audit tests.

Key Changes

1. Desktop Window Lifecycle & Synchronization:
   • Wired companion windows (\DocumentationWindow, \AiAssistWindow) with ownership (\Owner = MainWindow) for OS taskbar cohesion.
   • Synchronized minimize/restore lifecycle via \WindowSnapManager: minimizing MainWindow minimizes both attached and detached companions; restoring MainWindow restores companions and realigns attached ones.
   • Minimizing an attached companion window synchronizes MainWindow minimization.
   • Desktop tab buttons directly toggle native companion windows rather than opening in-app drawers.
2. Non-Modal Web Drawers:
   • Removed the blocking modal dimmer backdrop on Web so users can interact with the app while referencing documentation or chatting.
3. Responsive Collapsible Telemetry Header:
   • Added \IsCollapsed\ ribbon mode to \TelemetryHeaderControl\ collapsing into a slim 32px status ribbon with engine status indicators and a compact VRAM badge, preventing vertical crowding on mobile and horizontal tablets.
4. Responsive AI Assistant Chat UI:
   • Restructured header to wrap subtitle and status pills cleanly.
   • Replaced rigid 3-column setup wizard with an adaptive layout.
   • Stacked composer toolbar into two tiers (input + model selector on Tier 1, send/stop on Tier 2), eliminating button collisions at 440px width.
   • Added automated \AiAssistantTabControl_LayoutAudit\ covering 440px, 480px, and 1280px.
5. Adaptive Master-Detail Documentation:
   • Implemented responsive Master-Detail view for widths < 600px: full-width Topics list and full-width Detail view with \← Back to Topics\ button, eliminating horizontal text squishing.
   • Maintained two-column side-by-side view on wider screens (≥ 600px).
   • Added automated \DocumentationTabControl_LayoutAudit\ covering master and detail modes with 100/100 layout health.
6. Playwright Browser Automation with Video Recording:
   • Configured \PlaywrightScreenshotGenerator\ to record browser interaction sessions into \docs/images/videos/\ (.webm) and generate drawer screenshots.

Verification

• 
  pm run lint\ (0 errors)
• 
  px tsc --noEmit\ (0 errors)
• \dotnet test --filter 'FullyQualifiedName~AvaloniaLayoutAuditTests'\ (7/7 passed, 100/100 layout health score, 0 collisions, 0 boundary overflows)
• \dotnet test --filter 'FullyQualifiedName~PlaywrightScreenshotGenerator'\ (1/1 passed, video and screenshots generated)