💄(frontend) use official Marianne font

Updated styling system to implement the official French font used across all
La Suite products. This enhances brand consistency and improves the visual
identity alignment with other government digital services.

src/frontend/panda.config.ts

@@ -223,6 +223,7 @@ const config: Config = {
       fonts: {
         sans: {
           value: [
+            'Marianne',
             'Source Sans',
             'Source Sans fallback',
             'ui-sans-serif',