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
(CI, fresh clone, etc.):

  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 only 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 the 6.3.x line (6.3.9 is the last release before
the react-native peer was added). styled-components did not ship any
features between 6.3 and 6.4 that we were depending on, so the
rollback is a pure hygiene fix.

Verified with `rm -rf node_modules package-lock.json && npm install`
on all three plugins — resolves cleanly, strapi-plugin build and
strapi-plugin verify both pass.

Author: Schero94

package.json

@@ -82,7 +82,7 @@
     "react-dom": "^18.3.1",
     "react-router-dom": "^6.30.1",
     "semantic-release": "^25.0.3",
-    "styled-components": "^6.4.0"
+    "styled-components": "^6.3.9"
   },
   "peerDependencies": {
     "@strapi/sdk-plugin": "^5.4.0",