[nightshift] readme-improvements: add live URL header, browser support, AI dev section

[nightshift-micr]

Automated by Nightshift v3 (GLM 5.1).

Task: readme-improvements
Category: pr

Changes

• Live URL header: Added centered link to about.micr.dev at the top of the README
• Browser Support section: Documented desktop-only constraint with minimum viewport width
• Project Structure: Added .claude/skills/ entry to the directory tree
• How It Works: Clarified skeleton loader behavior (shimmer animation)
• Customization: Added note about JSON structure and displayName behavior
• AI-Assisted Development section: Documented the Claude Code ui-skills skill

Notes

The original README was already comprehensive — these are targeted additions that fill documentation gaps without restructuring.

Merge if useful, close if not.