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>

tests/widget-system/captcha-security-harness.php

@@ -88,6 +88,9 @@ namespace {
 	require dirname(__DIR__, 2) . '/inc/modules/captcha.php';
 	require dirname(__DIR__, 2) . '/src/Attachment/UploadLimits.php';
 	require dirname(__DIR__, 2) . '/src/Admin/Schema/SchemaPermissions.php';
+	require dirname(__DIR__, 2) . '/src/Core/Color.php';
+	require dirname(__DIR__, 2) . '/src/Admin/SchemaProviderOAuthValidation.php';
+	require dirname(__DIR__, 2) . '/src/Admin/SchemaProviderOptionMatch.php';
 	require dirname(__DIR__, 2) . '/src/Admin/SchemaProvider.php';
 
 	function check(bool $condition, string $message): void {