Add accessible interface font choices (#1306)

src/ui/tests/lib/ui-font.test.ts

@@ -0,0 +1,24 @@
+import { beforeEach, describe, expect, it } from "vitest";
+import { applyUiFont } from "../../lib/theme";
+
+describe("applyUiFont", () => {
+  beforeEach(() => {
+    localStorage.clear();
+    document.documentElement.style.removeProperty("--font-ui");
+  });
+
+  it("applies and persists a readable system font", () => {
+    applyUiFont("system-sans");
+
+    expect(document.documentElement.style.getPropertyValue("--font-ui")).toBe(
+      "ui-sans-serif, system-ui, sans-serif",
+    );
+    expect(localStorage.getItem("termix-ui-font")).toBe("system-sans");
+  });
+
+  it("falls back to JetBrains Mono for an unknown stored value", () => {
+    applyUiFont("unknown" as never);
+
+    expect(localStorage.getItem("termix-ui-font")).toBe("jetbrains-mono");
+  });
+});