[Preview] Add tablet and wide-screen device simulation presets

Problem

The built-in preview currently offers only a basic mobile device simulation toggle. There are no options for tablet (e.g., iPad, Galaxy Tab) or wide-screen / desktop viewports. This is a critical gap for any frontend developer working on responsive layouts.

Current Behavior

• Preview has a single "mobile" toggle — extremely limited.
• No way to simulate tablet viewports (768px–1024px range).
• No way to simulate specific wide-screen breakpoints (1280px, 1440px, 1920px).
• Developers are forced to leave the Claude Code app and use an external browser's DevTools to test responsive layouts — breaking the workflow entirely.

Expected Behavior

A device/viewport selector in the preview toolbar offering at minimum:

| Preset | Width | Use Case |
|--------|-------|----------|
| Mobile S | 320px | Small phones |
| Mobile M | 375px | iPhone SE / standard |
| Mobile L | 428px | iPhone Pro Max / large |
| Tablet Portrait | 768px | iPad / tablets vertical |
| Tablet Landscape | 1024px | iPad / tablets horizontal |
| Laptop | 1280px | Standard laptop |
| Desktop | 1440px | Common desktop |
| Wide | 1920px | Full HD monitors |
| Custom | User-defined | Any specific size |

Why This Matters

• Responsive design is not optional — modern web projects must work across all screen sizes.
• Tailwind CSS (the most popular utility framework) uses breakpoints at sm:640, md:768, lg:1024, xl:1280, 2xl:1536 — developers need to verify each one.
• Without tablet/desktop presets, the preview tool is essentially unusable for professional responsive development.
• Being forced to switch to an external browser DevTools defeats the purpose of having an integrated preview.

Suggested Implementation

• A dropdown or segmented control in the preview toolbar: 📱 Mobile | 📱 Tablet | 💻 Desktop | 🖥 Wide | ⚙ Custom
• Each preset sets the viewport width/height accordingly.
• A "Custom" option with manual width × height input fields.
• Optionally show the current viewport dimensions as a label (e.g., "390 × 844").

Environment

• Claude Code Desktop App (Windows 11)
• Daily professional use for responsive frontend development (Next.js / Tailwind CSS)