feat(theme): persistent light/dark toggle in the titlebar

src/store/useTheme.ts

@@ -0,0 +1,16 @@
+import { create } from "zustand";
+import { applyTheme, initialTheme, type Theme } from "../theme";
+
+interface ThemeState {
+  theme: Theme;
+  toggle: () => void;
+}
+
+export const useTheme = create<ThemeState>((set, get) => ({
+  theme: initialTheme(),
+  toggle: () => {
+    const next: Theme = get().theme === "dark" ? "light" : "dark";
+    applyTheme(next);
+    set({ theme: next });
+  },
+}));