feat: custom CSS editor with CodeMirror, live preview, and /docs/css reference

thoughts-frontend/package.json

@@ -9,6 +9,7 @@
     "lint": "eslint"
   },
   "dependencies": {
+    "@codemirror/lang-css": "^6.3.1",
     "@hookform/resolvers": "^5.2.1",
     "@radix-ui/react-accordion": "^1.2.12",
     "@radix-ui/react-alert-dialog": "^1.1.15",
@@ -37,6 +38,7 @@
     "@radix-ui/react-toggle-group": "^1.1.11",
     "@radix-ui/react-tooltip": "^1.2.8",
     "@types/js-cookie": "^3.0.6",
+    "@uiw/react-codemirror": "^4.25.10",
     "class-variance-authority": "^0.7.1",
     "clsx": "^2.1.1",
     "cmdk": "^1.1.1",