Expand CSS Variables tab to full variable reference and add custom-hero class

- Replace 8-field CSS Variables tab with 21 comprehensive sections covering
  all variables from light.standard.css and dark.standard.css
- New sections: Links, Layout & Spacing, Breakpoints, Bootstrap Semantic
  Palette, Bootstrap State Colors, Alert & List Group Colors, Standard
  Colors/Grays/Opacity, Shadows & Shadow Tokens, Buttons, Cards,
  Component & Plugin Colors, VirtueMart, Gable
- Add custom-hero class to hero.php outer div (always present)
- Both en-GB and en-US language files updated

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

src/media/css/template.css

@@ -14091,6 +14091,8 @@ meter {
 	background-attachment: fixed;
 	background-position: top, center;
 	background-size: cover;
+	border-bottom: solid var(--accent-color-secondary);
+
 }
 
 .container-banner .banner-overlay .overlay {