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/WidgetSystem/FieldSchema.php

@@ -79,7 +79,7 @@ final class FieldSchema {
 			case 'upload':
 				return esc_url_raw((string) $value);
 			case 'color':
-				return self::color((string) $value);
+				return \AKSRT\Core\Color::sanitize($value, true);
 			case 'icon':
 				return function_exists('aksrt_sanitize_icon_value')
 					? aksrt_sanitize_icon_value((string) $value)
@@ -192,7 +192,7 @@ final class FieldSchema {
 	private static function background($value): array {
 		$value = is_array($value) ? $value : [];
 		return [
-			'color'      => self::color((string) ($value['color'] ?? '')),
+			'color'      => \AKSRT\Core\Color::sanitize($value['color'] ?? '', true),
 			'image'      => esc_url_raw((string) ($value['image'] ?? '')),
 			'position'   => self::allow((string) ($value['position'] ?? 'center center'), ['center center', 'top center', 'bottom center', 'center left', 'center right'], 'center center'),
 			'repeat'     => self::allow((string) ($value['repeat'] ?? 'no-repeat'), ['no-repeat', 'repeat', 'repeat-x', 'repeat-y'], 'no-repeat'),
@@ -213,18 +213,6 @@ final class FieldSchema {
 		return self::normalize($children, is_array($value) ? $value : []);
 	}
 
-	private static function color(string $value): string {
-		$value = trim($value);
-		if ($value === '') {
-			return '';
-		}
-		$hex = sanitize_hex_color($value);
-		if ($hex) {
-			return $hex;
-		}
-		return preg_match('/^rgba?\(\s*\d{1,3}\s*,\s*\d{1,3}\s*,\s*\d{1,3}(?:\s*,\s*(?:0|1|0?\.\d+))?\s*\)$/', $value) ? $value : '';
-	}
-
 	private static function allow(string $value, array $allowed, string $fallback): string {
 		return in_array($value, $allowed, true) ? $value : $fallback;
 	}

src/WidgetSystem/FormRenderer.php

@@ -221,7 +221,7 @@ final class FormRenderer {
 
 	private static function background(SchemaWidget $widget, string $key, array $value): void {
 		echo '<div class="aksrt-widget-background">';
-		self::plain_input($widget, $key . '[color]', (string) ($value['color'] ?? ''), 'text', '背景颜色');
+		self::plain_input($widget, $key . '[color]', (string) ($value['color'] ?? ''), 'text', '背景颜色', 'widefat aksrt-widget-color');
 		self::plain_input($widget, $key . '[image]', (string) ($value['image'] ?? ''), 'url', '背景图片 URL');
 		foreach ([
 			'position' => ['center center' => '居中', 'top center' => '顶部', 'bottom center' => '底部', 'center left' => '左侧', 'center right' => '右侧'],
@@ -273,9 +273,9 @@ final class FormRenderer {
 		echo '</div></details>';
 	}
 
-	private static function plain_input(SchemaWidget $widget, string $key, string $value, string $type, string $placeholder): void {
+	private static function plain_input(SchemaWidget $widget, string $key, string $value, string $type, string $placeholder, string $class = 'widefat'): void {
 		$name = $widget->get_field_name($key);
 		$id   = $widget->get_field_id(str_replace(['[', ']'], ['-', ''], $key));
-		echo '<input class="widefat" type="' . esc_attr($type) . '" id="' . esc_attr($id) . '" name="' . esc_attr($name) . '" value="' . esc_attr($value) . '" placeholder="' . esc_attr($placeholder) . '">';
+		echo '<input class="' . esc_attr($class) . '" type="' . esc_attr($type) . '" id="' . esc_attr($id) . '" name="' . esc_attr($name) . '" value="' . esc_attr($value) . '" placeholder="' . esc_attr($placeholder) . '">';
 	}
 }