feat: dark/light theming system + design tokens (OMC design system port)

- Restructure design tokens into :root/.dark raw vars mapped via @theme inline
- Add light/dark/system theming: useTheme hook + FOUC guard + ThemeToggle
- Keep iamcavalli palette (primary #1A463C, accent #DEF168) and Geist fonts
- Derive brand-consistent dark palette (verde-nero bg, lightened primary)
- Add scrollbar utilities (.no-scrollbar/.thin-scrollbar)
- Install tailwindcss-animate, register via @plugin (Tailwind v4)
- Mount ThemeToggle in admin sidebar footer

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

package-lock.json

@@ -33,6 +33,7 @@
         "react-dom": "19.2.4",
         "react-hook-form": "^7.75.0",
         "tailwind-merge": "^3.6.0",
+        "tailwindcss-animate": "^1.0.7",
         "zod": "^4.4.3"
       },
       "devDependencies": {
@@ -9308,9 +9309,17 @@
       "version": "4.3.0",
       "resolved": "https://registry.npmjs.org/tailwindcss/-/tailwindcss-4.3.0.tgz",
       "integrity": "sha512-y6nxMGB1nMW9R6k96e5gdIFzcfL/gTJRNaqGes1YvkLnPVXzWgbqFF2yLC0T8G774n24cx3Pe8XrKoniCOAH+Q==",
-      "dev": true,
       "license": "MIT"
     },
+    "node_modules/tailwindcss-animate": {
+      "version": "1.0.7",
+      "resolved": "https://registry.npmjs.org/tailwindcss-animate/-/tailwindcss-animate-1.0.7.tgz",
+      "integrity": "sha512-bl6mpH3T7I3UFxuvDEXLxy/VuFxBk5bbzplh7tXI68mwMokNYd1t9qPBHlnyTwfa4JGC4zP516I1hYYtQ/vspA==",
+      "license": "MIT",
+      "peerDependencies": {
+        "tailwindcss": ">=3.0.0 || insiders"
+      }
+    },
     "node_modules/tapable": {
       "version": "2.3.3",
       "resolved": "https://registry.npmjs.org/tapable/-/tapable-2.3.3.tgz",