Tighten mobile viewer layout for phones

[tridha643]

Summary

• Add mobile overflow assertions to E2E helpers and cover the main native surface primitives on an iPhone-sized viewport
• Rework the session timeline for small screens with compact fold controls, wrapped command rows, and better spacing
• Adjust viewer and embed styles to prevent horizontal overflow and improve touch ergonomics on mobile

Screenshots

Mobile timeline / iPhone 14 Pro viewport:

Testing

• Added Playwright UI coverage for mobile trace, timeline, and primitive rendering
• Added viewport-specific overflow checks for frames and core page containers