Improve Indexes chapter organization and harmonization

- Add YAML frontmatter with title, authors, and date metadata
- Add Learning Objectives admonition at the beginning
- Add Prerequisites section linking to related chapters
- Reorganize content with clearer section hierarchy
- Add proper admonition formatting (tip, note, warning, important)
- Integrate SQL examples naturally as reference section
- Improve quiz formatting with dropdown answer
- Add comprehensive Summary section with next steps
- Remove broken SQL execution section at the end
- Add tables for index mechanisms and query patterns

Author: claude