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>

assets/js/gutenberg-blocks.js

@@ -23,7 +23,6 @@
   var InnerBlocks = blockEditor.InnerBlocks || null;
   var RichText = blockEditor.RichText || null;
   var MediaUpload = blockEditor.MediaUpload || null;
-  var ColorPicker = wp.components.ColorPicker;
   var PanelBody = wp.components.PanelBody;
   var SelectControl = wp.components.SelectControl;
   var TextControl = wp.components.TextControl;