update frontend

static/app.js

@@ -10,6 +10,21 @@ marked.setOptions({
     mangle: false,
 });
 
+// ---- Theme ----
+function initTheme() {
+    const saved = localStorage.getItem('rag-theme') || 'dark';
+    document.documentElement.setAttribute('data-theme', saved);
+}
+
+function toggleTheme() {
+    const current = document.documentElement.getAttribute('data-theme');
+    const next = current === 'dark' ? 'light' : 'dark';
+    document.documentElement.setAttribute('data-theme', next);
+    localStorage.setItem('rag-theme', next);
+}
+
+initTheme();
+
 // DOM
 const sessionList = document.getElementById('session-list');
 const messages = document.getElementById('messages');
@@ -21,6 +36,7 @@ const btnNewSession = document.getElementById('btn-new-session');
 const btnClear = document.getElementById('btn-clear');
 const btnDelete = document.getElementById('btn-delete');
 const btnMenu = document.getElementById('btn-menu');
+const btnTheme = document.getElementById('btn-theme');
 const chatTitle = document.getElementById('chat-title');
 const statsEl = document.getElementById('stats');
 
@@ -232,6 +248,7 @@ btnNewSession.onclick = createSession;
 btnClear.onclick = clearMessages;
 btnDelete.onclick = deleteSession;
 btnSend.onclick = sendMessage;
+btnTheme.onclick = toggleTheme;
 
 btnMenu.onclick = () => {
     document.getElementById('sidebar').classList.toggle('open');