docs: rewrite CONTRIBUTING.md to encourage early user feedback

Restructure contributing guide to prioritize user engagement and feedback
over developer contributions, emphasizing the main motivation for early
publication: getting the library into users' hands to shape development.

Key changes:
- Lead with "Why Publish Early?" - emphasize feedback-driven development
- Add "We Want to Hear From You" section with clear feedback categories
- Include Quick Start section with working examples (no API key + with API key)
- Link prominently to GitHub Discussions for feedback
- Show what's currently working (113 operations, 65% coverage)
- Move developer contribution guidelines to second half
- Update guidelines to reference CLAUDE.md for comprehensive rules
- Add testing tier structure (public/location/portal)
- Include all just recipes with descriptions
- Simplify and clarify workflow for new contributors

Audience shift:
- Primary: Users trying the library and providing feedback
- Secondary: Developers contributing code

Goal: Make it easy for anyone to:
1. Try the library in 60 seconds
2. Share their experience
3. Report what works and what doesn't
4. Understand the development roadmap

Files modified:
- CONTRIBUTING.md - Complete rewrite prioritizing user engagement

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude Sonnet 4.5 <noreply@anthropic.com>

Author: crumplecup