chore: alphabetize entries within each section

Sorts list entries alphabetically by link text (case-insensitive) within
every section of the README. The `## Contents` TOC is left untouched
since its order must match the section sequence.

Also normalizes 3 malformed entries that had a double-space after the
dash (`-  [Name]` → `- [Name]`).

No entries added, removed, or reworded. 136 groups sorted.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>