refactor(theme-settings): remove CSS card, CSS now managed by CustomCSSManager

- Remove custom_css field from schema (v1.4.0 → v1.5.0)
- Remove buildCssGroup() from FormBuilder
- Remove renderCustomCSS() from Renderer
- Update layout: single JS card instead of 2-column layout
- Update descriptions to reference CustomCSSManager (TIPO 3)

CSS personalizado ahora se gestiona exclusivamente desde el
componente CustomCSSManager, eliminando duplicidad funcional.

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude <noreply@anthropic.com>

Schemas/theme-settings.json

@@ -1,7 +1,7 @@
 {
   "component_name": "theme-settings",
-  "version": "1.4.0",
-  "description": "Configuraciones globales del tema: layout y codigo personalizado",
+  "version": "1.5.0",
+  "description": "Configuraciones globales del tema: layout y JavaScript personalizado",
   "groups": {
     "layout": {
       "label": "Layout y Contenedor",
@@ -37,16 +37,9 @@
       }
     },
     "custom_code": {
-      "label": "Codigo Personalizado",
+      "label": "JavaScript Personalizado",
       "priority": 10,
       "fields": {
-        "custom_css": {
-          "type": "textarea",
-          "label": "CSS Personalizado",
-          "default": "",
-          "editable": true,
-          "description": "CSS personalizado que se inyecta en wp_head. No incluir etiquetas <style>"
-        },
         "custom_js_header": {
           "type": "textarea",
           "label": "JavaScript en Header",