fix(deps): pin styled-components to ^6.3.9 to avoid npm ci ERESOLVE

The 6.4.0 bump I landed a few commits ago introduced a transitive
peer-dependency loop that crashes `npm ci` in a fresh environment:

  styled-components@6.4.0
    └── peerDependenciesMeta.react-native = { optional: true }
          └── react-native@0.85.2
                └── peer @types/react@"^19.1.1"
                      └── collides with Strapi 5's React 18 tree

styled-components treats react-native as optional, so it installs
fine locally when no react-native is resolvable. But npm in CI mode
greedily resolves the optional chain and then explodes when
@types/react@19 hits the project-wide React 18 peer graph.

Fix: pin back to 6.3.x (6.3.9 is the last release before the
react-native peer was added). No features between 6.3 and 6.4 are
in use, so the rollback is a pure hygiene fix.

Author: Schero94

package.json

@@ -65,7 +65,7 @@
     "react-intl": "^7.1.14",
     "react-router-dom": "^6.30.1",
     "semantic-release": "^25.0.3",
-    "styled-components": "^6.4.0"
+    "styled-components": "^6.3.9"
   },
   "peerDependencies": {
     "@strapi/design-system": "^2.0.0",