Update README with user-focused feature documentation

Complete rewrite of README to focus on user capabilities and workflows:

Structure:
- Clear quick start with immediate value examples
- Feature-organized sections (not command-by-command)
- Real-world workflow examples
- Comprehensive configuration reference

New Features Documented:
- forest write: AI-powered long-form content generation
- forest node synthesize: Combine multiple notes into new perspectives
- forest node recent: Activity timeline for tracking changes
- forest config: Interactive configuration wizard
- LLM-powered tagging with GPT-5-nano
- Transparent document chunking for large documents
- TLDR v0.2 agent discovery with --tldr=all
- --raw flag for pipeable markdown output

Improvements:
- Organized by user intent (capture, search, manage) vs alphabetical commands
- Common workflows section with practical examples
- No emojis, professional tone
- Balanced between concise and informative
- Highlights both CLI and API capabilities
- Clear embedding provider documentation
- Configuration variables reference

Removes:
- Outdated command references (insights → edges)
- Version 0.1.0 header
- Overly technical implementation details

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

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

Author: bwl