Load Inter via Fontsource and set mono stack

Self-host the Inter variable font through @fontsource-variable/inter
rather than a CDN, so the v2 type scale renders in Inter with no
third-party request. Import it from the theme and point --font-sans
at the "Inter Variable" family the package registers.

Add --font-mono as a Radix-style system stack: the design specifies
Menlo, an Apple system font that cannot be self-hosted, so it falls
back per OS (Consolas, Liberation Mono, Monaco, monospace).

Signed-off-by: Émile Ré <emile@probo.com>

packages/ui/package.json

@@ -14,6 +14,7 @@
   "dependencies": {
     "@ariakit/react": "^0.4.17",
     "@floating-ui/react": "^0.27.19",
+    "@fontsource-variable/inter": "^5.2.8",
     "@phosphor-icons/react": "^2.1.10",
     "@probo/helpers": "1.0.0",
     "@probo/i18n": "1.0.0",