Align skill descriptions with Anthropic best practices

Update all SKILL.md descriptions to lead with what the skill does
(third person) followed by trigger conditions, per Anthropic's
skill authoring docs. All original trigger conditions preserved.
Update description max chars to match Anthropic spec (1024).
Retain workflow-summary warning in skill-anatomy.md to prevent
agents from following descriptions instead of reading full skills.
Add Table of Contents to reference files longer than 100 lines so
Claude can see the full scope of available information even when
previewing with partial reads.

references/accessibility-checklist.md

@@ -2,6 +2,14 @@
 
 Quick reference for WCAG 2.1 AA compliance. Use alongside the `frontend-ui-engineering` skill.
 
+## Table of Contents
+
+- [Essential Checks](#essential-checks)
+- [Common HTML Patterns](#common-html-patterns)
+- [Testing Tools](#testing-tools)
+- [Quick Reference: ARIA Live Regions](#quick-reference-aria-live-regions)
+- [Common Anti-Patterns](#common-anti-patterns)
+
 ## Essential Checks
 
 ### Keyboard Navigation