Fix a11y icon, FAB label colors, add high-contrast stylesheet, sync theme vars

- Fix faIcon() to use <i> elements (FA7 compatibility)
- Fix #mokoThemeFab .label and button colors to white (visible on
  both light and dark themes)
- Fix font-weight typo (600px → 600)
- Add --footer-padding-* variables to all 6 theme files
- Create a11y-high-contrast.css with WCAG AAA contrast ratios for
  both light and dark modes
- Register high-contrast stylesheet in joomla.asset.json
- Lazy-load high-contrast CSS when a11y contrast toggle is activated

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

src/joomla.asset.json

@@ -124,6 +124,12 @@
 			"uri": "media/templates/site/mokocassiopeia/css/theme/dark.custom.min.css",
 			"attributes": {"media": "all"}
 		},
+		{
+			"name": "template.a11y-high-contrast",
+			"type": "style",
+			"uri": "media/templates/site/mokocassiopeia/css/a11y-high-contrast.css",
+			"attributes": {"media": "all"}
+		},
 		{
 			"name": "template.js",
 			"type": "script",