refactor(color): unify color sanitizing and picking behind shared components

- Add AKSRT\Core\Color::sanitize($value, $allow_alpha) as the single PHP
  color sanitizer; replace sanitize_hex_color calls and per-class regexes
  (FloatButtons, FieldSchema, ThemeSearch, icon cards, TicketStatusService)
- SchemaProvider / ControllerBase sanitize `color` fields as colors;
  alpha kept only when the schema sets showAlpha
- Split SchemaProvider OAuth validation and option matching into sibling
  traits to stay under the 1000-line limit
- Add AksColorPicker.vue + utils/color.js mirroring the PHP rules; AksField,
  FloatBtnCommonFields and TicketStatusPanel use it
- Widget background color input now uses wpColorPicker
- Remove dead AksCompositeField dimensions/spacing/background branches and
  the unused Gutenberg ColorPicker var
- Add color-unification contract test; update harness requires and tests

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

src/Settings/HomeCms.php

@@ -61,9 +61,9 @@ class HomeCms {
 		$s = self::get_footer_settings();
         return [
             'custom'       => !empty($s['footer_theme_custom']),
-            'bg_custom'    => sanitize_hex_color((string) ($s['footer_theme_bg_custom'] ?? '')) ?: '',
+            'bg_custom'    => \AKSRT\Core\Color::sanitize((string) ($s['footer_theme_bg_custom'] ?? '')) ?: '',
 			'bg'           => self::normalize_palette_hex((string) ($s['footer_theme_bg'] ?? '')),
-            'color_custom' => sanitize_hex_color((string) ($s['footer_theme_color_custom'] ?? '')) ?: '',
+            'color_custom' => \AKSRT\Core\Color::sanitize((string) ($s['footer_theme_color_custom'] ?? '')) ?: '',
         ];
     }