chore(Demo): Add back Tengwar font (#10147)

This adds back the Tengwar font to support an upcoming complete and
maintained translation into Sindarin, powered by Claude Code and
automated workflows.

This is even less invasive than the method I had originally. It does not
touch the library CSS at all.

demo/demo.less

@@ -81,6 +81,21 @@ html, body {
   font-family: Roboto, sans-serif;
 }
 
+// This font supports the Sindarin (sjn) translation.
+@font-face {
+  // The Tengwar Telcontar font
+  // From https://freetengwar.sourceforge.net/tengtelc.html
+  src: url("../demo/TengwarTelcontar.woff2") format("woff2");
+  // Unicode Private Use Area (PUA) used by ConScript Unicode Registry (CSUR)
+  // to represent Tengwar glyphs.  This will keep the font from being loaded
+  // for any other codepoints.
+  unicode-range: U+E000-E0FF;
+  // Fun trick to avoid hard-coding Tengwar support into the library:
+  // Add this font for these codepoint ranges in anything that uses "Roboto",
+  // without having to modify the CSS to point at another font family.
+  font-family: Roboto;
+}
+
 /* Change the default opacity of the ripple container, to get around an iOS bug.
  * See: https://github.com/google/material-design-lite/issues/5281 */
 .mdl-ripple {