Add col-5ths responsive columns and Width_Group JS utility

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude <noreply@anthropic.com>

docs/CLAUDE.dist.md

@@ -434,6 +434,7 @@ Pattern recognition:
 - Tier 2: `phone`, `tablet`, `desktop-sm`, `desktop-md`, `desktop-lg`, `desktop-xl`
 - SCSS: `@include mobile { }`, `@include desktop-xl { }`
 - Classes: `.col-mobile-12`, `.d-tablet-none`, `.mobile-only`
+- Fifth-width columns: `.col-5ths`, `.col-mobile-5ths`, `.col-desktop-5ths`, etc.
 - JS: `Responsive.is_mobile()`, `Responsive.is_phone()`
 
 **Detailed guidance in `scss` skill** - auto-activates when styling components.