♻️(app-desk) improve useCunninghamTheme

Some tokens were not available from the hook.

We only had the tokens of the currentTheme available
but actually the theme is an augmentation of the
default theme, so we should use the default theme
tokens as a base and then override them with the
currentTheme tokens.
It is what this commit does.

src/frontend/apps/desk/package.json

@@ -18,6 +18,7 @@
     "@openfun/cunningham-react": "2.6.0",
     "@tanstack/react-query": "5.25.0",
     "i18next": "23.10.1",
+    "lodash": "4.17.21",
     "luxon": "3.4.4",
     "next": "14.1.3",
     "react": "18.2.0",
@@ -34,6 +35,7 @@
     "@testing-library/react": "14.2.1",
     "@testing-library/user-event": "14.5.2",
     "@types/jest": "29.5.12",
+    "@types/lodash": "4.14.202",
     "@types/luxon": "3.4.2",
     "@types/node": "*",
     "@types/react": "18.2.64",