feat(ui): add light theme toggle

src/lib/ui/theme.test.ts

@@ -0,0 +1,35 @@
+import { describe, expect, test } from "vitest";
+import {
+  getNextUiTheme,
+  isUiTheme,
+  resolveInitialUiTheme,
+  UI_THEME_STORAGE_KEY,
+} from "./theme";
+
+describe("UI theme preference", () => {
+  test("defaults to dark when no stored preference exists", () => {
+    const storage = new Map<string, string>();
+
+    expect(resolveInitialUiTheme(storage)).toBe("dark");
+  });
+
+  test("restores a valid stored preference", () => {
+    const storage = new Map<string, string>([[UI_THEME_STORAGE_KEY, "light"]]);
+
+    expect(resolveInitialUiTheme(storage)).toBe("light");
+  });
+
+  test("ignores invalid stored preferences", () => {
+    const storage = new Map<string, string>([[UI_THEME_STORAGE_KEY, "solarized"]]);
+
+    expect(resolveInitialUiTheme(storage)).toBe("dark");
+  });
+
+  test("detects and toggles supported themes", () => {
+    expect(isUiTheme("light")).toBe(true);
+    expect(isUiTheme("dark")).toBe(true);
+    expect(isUiTheme("contrast")).toBe(false);
+    expect(getNextUiTheme("dark")).toBe("light");
+    expect(getNextUiTheme("light")).toBe("dark");
+  });
+});