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/GlobalController.php

@@ -365,8 +365,8 @@ class GlobalController extends ControllerBase {
             'icon_size'         => max(16, min(32, (int) ($params['icon_size'] ?? 22))),
             'text_size'         => max(8, min(14, (int) ($params['text_size'] ?? 10))),
             'show_text'         => !empty($params['show_text']),
-            'active_color'      => sanitize_hex_color($params['active_color'] ?? '') ?: '#f04494',
-            'bg_color'          => sanitize_hex_color($params['bg_color'] ?? '') ?: '',
+            'active_color'      => \AKSRT\Core\Color::sanitize($params['active_color'] ?? '') ?: '#f04494',
+            'bg_color'          => \AKSRT\Core\Color::sanitize($params['bg_color'] ?? '') ?: '',
             'border'            => !empty($params['border']),
             'shadow'            => !empty($params['shadow']),
             'animation'         => !empty($params['animation']),