Use native system fonts on Android and iOS

This behavior is called for in the new designs, but Compound Web doesn't (yet) implement it by default.

src/index.css

@@ -25,12 +25,6 @@ limitations under the License.
 @import "@vector-im/compound-web/dist/style.css";
 
 :root {
-  --font-family: "Inter", -apple-system, BlinkMacSystemFont, "Segoe UI",
-    "Roboto", "Oxygen", "Ubuntu", "Cantarell", "Fira Sans", "Droid Sans",
-    "Helvetica Neue", sans-serif;
-  --inter-unicode-range: U+0000-20e2, U+20e4-23ce, U+23d0-24c1, U+24c3-259f,
-    U+25c2-2664, U+2666-2763, U+2765-2b05, U+2b07-2b1b, U+2b1d-10FFFF;
-
   --font-scale: 1;
   --font-size-micro: calc(10px * var(--font-scale));
   --font-size-caption: calc(12px * var(--font-scale));
@@ -149,7 +143,6 @@ body {
   color: var(--cpd-color-text-primary);
   color-scheme: dark;
   margin: 0;
-  font-family: var(--font-family);
   -webkit-font-smoothing: antialiased;
   -moz-osx-font-smoothing: grayscale;
 }
@@ -165,6 +158,19 @@ body,
   flex-direction: column;
 }
 
+/* On Android and iOS, prefer native system fonts */
+body[data-platform="android"] {
+  --cpd-font-family-sans: "Roboto", "Noto", "Inter", sans-serif;
+}
+
+body[data-platform="ios"] {
+  --cpd-font-family-sans: -apple-system, BlinkMacSystemFont, "Inter", sans-serif;
+}
+
+body[data-platform="desktop"] {
+  --cpd-font-family-sans: "Inter", sans-serif;
+}
+
 h1,
 h2,
 h3,