Rewrite agent-model-matching.md as a technical reference that:
- Documents actual fallback chains from model-requirements.ts
- Explains model-specific prompt routing (Prometheus/Atlas GPT detection)
- Covers safe vs dangerous model substitutions with rationale
- Includes task categories (visual-engineering, deep, quick, etc.)
- Guides agents on how to explain model choices to users
- Adds provider priority chain
Also update installation.md to reference the guide when users
want custom model configuration, with explanation of what is
safe to change and why.
- Add docs/guide/agent-model-matching.md with TL;DR table, detailed
breakdown per agent, configuration examples, decision tree, common
pitfalls, and default fallback chains
- Update README.md to reference the guide in TOC, Just Install This
section, and Features overview
