style(frontend): redesign with Miuix HyperOS design language

- Color system: Miuix dark tokens (primary #277AF7, bg #242424, surface #000)
- Components: rounded-full buttons, squircle cards (18px), glass header
- Messages: blue user bubbles, dark AI bubbles with typing animation
- Admin dashboard: stat cards with real-time service status
- Login: centered logo with gradient shadow, HyperOS input fields
- Smooth transitions and scale-on-press interactions

frontend/web/src/components/layout/Sidebar.tsx

@@ -16,18 +16,22 @@ export default function Sidebar() {
   }
 
   return (
-    <aside className="w-56 bg-gray-900 border-r border-gray-800 flex flex-col shrink-0">
+    <aside className="w-60 bg-[#000] border-r border-[#393939] shrink-0 flex flex-col">
       <div className="p-3">
         <button onClick={handleNewChat}
-          className="w-full py-2 bg-purple-600 hover:bg-purple-500 rounded text-sm font-medium transition-colors">
+          className="w-full py-2.5 bg-[#277AF7] hover:bg-[#3482FF] active:scale-[0.98] text-white font-medium text-sm rounded-full transition-all duration-200"
+        >
           + 新对话
         </button>
       </div>
-      <div className="flex-1 overflow-auto px-2 text-sm text-gray-400">
+
+      <div className="flex-1 overflow-auto px-2 pb-2">
         {currentSessionId ? (
-          <p className="px-2 py-1 truncate text-xs">会话: {currentSessionId.slice(0, 8)}...</p>
+          <div className="px-3 py-2 bg-[#242424] rounded-[14px]">
+            <p className="text-xs text-white/40 truncate">{currentSessionId.slice(0, 12)}...</p>
+          </div>
         ) : (
-          <p className="px-2 py-1 text-xs">暂无对话</p>
+          <p className="px-3 py-2 text-xs text-white/30 text-center">暂无对话</p>
         )}
       </div>
     </aside>