feat: complete UI overhaul (liquid glass theme, i18n, FontAwesome)

src/lib/theme.tsx

@@ -0,0 +1,52 @@
+import React, { createContext, useContext, useEffect, useState, ReactNode } from 'react';
+
+type Theme = 'light' | 'dark';
+
+interface ThemeContextType {
+  theme: Theme;
+  toggleTheme: () => void;
+}
+
+const ThemeContext = createContext<ThemeContextType | null>(null);
+
+export function ThemeProvider({ children }: { children: ReactNode }) {
+  const [theme, setTheme] = useState<Theme>(() => {
+    try {
+      const stored = localStorage.getItem('melodymuse-theme');
+      if (stored === 'light' || stored === 'dark') return stored;
+    } catch {
+      // ignore
+    }
+    return window.matchMedia('(prefers-color-scheme: light)').matches ? 'light' : 'dark';
+  });
+
+  useEffect(() => {
+    const root = window.document.documentElement;
+    if (theme === 'dark') {
+      root.classList.add('dark');
+    } else {
+      root.classList.remove('dark');
+    }
+    try {
+      localStorage.setItem('melodymuse-theme', theme);
+    } catch {
+      // ignore
+    }
+  }, [theme]);
+
+  const toggleTheme = () => {
+    setTheme((prev) => (prev === 'dark' ? 'light' : 'dark'));
+  };
+
+  return (
+    <ThemeContext.Provider value={{ theme, toggleTheme }}>
+      {children}
+    </ThemeContext.Provider>
+  );
+}
+
+export function useTheme() {
+  const ctx = useContext(ThemeContext);
+  if (!ctx) throw new Error('useTheme must be used within ThemeProvider');
+  return ctx;
+}