feat: add a white theme

lib/theme.tsx

@@ -0,0 +1,49 @@
+"use client";
+
+import { createContext, useContext, useEffect, useState } from "react";
+
+type Theme = "dark" | "light";
+
+interface ThemeContextType {
+    theme: Theme;
+    toggle: () => void;
+}
+
+const ThemeContext = createContext<ThemeContextType>({
+    theme: "dark",
+    toggle: () => {},
+});
+
+export function ThemeProvider({ children }: { children: React.ReactNode }) {
+    const [theme, setTheme] = useState<Theme>("dark");
+
+    useEffect(() => {
+        const stored = localStorage.getItem("wyview-theme") as Theme | null;
+        if (stored) setTheme(stored);
+    }, []);
+
+    useEffect(() => {
+        const root = document.documentElement;
+        if (theme === "light") {
+            root.classList.add("light");
+            root.classList.remove("dark");
+        } else {
+            root.classList.add("dark");
+            root.classList.remove("light");
+        }
+        localStorage.setItem("wyview-theme", theme);
+    }, [theme]);
+
+    const toggle = () => setTheme((t) => (t === "dark" ? "light" : "dark"));
+
+    return (
+        <ThemeContext.Provider value={{ theme, toggle }}>
+            {children}
+        </ThemeContext.Provider>
+    );
+}
+
+export function useTheme() {
+    return useContext(ThemeContext);
+}
+