Add google-stitch skill

[Zenlyte]

Description

Adds Google Stitch integration - generates UI screens from text prompts using the @google/stitch-sdk package.

Features

• Create and manage Stitch projects
• Generate mobile/web screens from text prompts
• Export HTML and screenshots
• Edit existing screens and generate variants
• CLI tool with 12 commands

Testing

• bun validate passes with no errors
• Verified API key authentication works
• Tested project creation, screen generation, and HTML/screenshot export

Checklist

• SKILL.md has required frontmatter (name, description, metadata.author)
• Skill directory name matches name in frontmatter
• Description clearly explains when to use the skill
• No sensitive data (API keys, tokens) included
• bun validate passes

[skeletor-js]

Please clean this up before resubmitting.

• Replace the placeholder author field.
• Clarify the dependency/runtime expectations for the SDK usage in this skill.
• Make sure the skill can be understood and installed cleanly by someone who does not share your local setup.
• Do a final pass on completeness and packaging.