docs: update index + related pages for v0.27.0 starter-train changes
docs(wiki): split Features into per-feature subpages Features.md now summarises each feature and links to a dedicated page. Detail content moves into nine Feature-*.md files, one per feature, so each feature is easier to link to and edit in isolation. No content is lost; cross-page links have been updated. Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>