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/Admin/ControllerBase.php

@@ -108,6 +108,12 @@ abstract class ControllerBase {
 					$ids = is_array($val) ? array_filter(array_map('absint', $val)) : [];
 					$out[$key] = array_values(array_unique($ids));
 					break;
+				case 'color':
+					$out[$key] = \AKSRT\Core\Color::sanitize($val);
+					break;
+				case 'color_alpha':
+					$out[$key] = \AKSRT\Core\Color::sanitize($val, true);
+					break;
                 default:
                     $out[$key] = sanitize_text_field($val);
             }