docs: remove extraneous content — pipeline internals moved to architecture, changelog removed
- features.md: remove SQL impl detail from tasks section, sw.js reference from PWA section,
and entire "LLM Chat — Internal Pipeline" section (moved to architecture.md)
- architecture.md: add "LLM Pipeline Internals" section (intent routing, tool loop, duplicate
guards, context window, research pipeline, image cache)
- development.md: remove site-specific NFS path from custom runner instructions
- Remove changelog.md (duplicates git history)
- README.md: remove changelog link
Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>