feat(web): 构建漂流瓶移动端 PWA

- 演示登录、内存令牌、单 Promise 刷新与路由守卫\n- 投瓶、捞瓶、首次回复、会话与实时聊天\n- 独立管理员登录与审核/举报工作台\n- Socket 认证续期、断线补齐与账号切换清理\n- PWA 离线壳、深海主题与移动端无障碍

apps/web/public/icon.svg

@@ -0,0 +1 @@
+<svg xmlns="http://www.w3.org/2000/svg" viewBox="0 0 512 512"><rect width="512" height="512" rx="112" fill="#061b2b"/><circle cx="256" cy="210" r="128" fill="#0b4050"/><path d="M180 130h152l-20 196c-5 48-107 48-112 0z" fill="#76e4d5" opacity=".85"/><path d="M160 350q96-70 192 0" fill="none" stroke="#f1c27d" stroke-width="22" stroke-linecap="round"/></svg>

apps/web/public/manifest.webmanifest

@@ -0,0 +1,16 @@
+{
+  "name": "漂流瓶 · 深海回声",
+  "short_name": "漂流瓶",
+  "start_url": "/",
+  "display": "standalone",
+  "background_color": "#04111d",
+  "theme_color": "#061b2b",
+  "icons": [
+    {
+      "src": "/icon.svg",
+      "sizes": "any",
+      "type": "image/svg+xml",
+      "purpose": "any maskable"
+    }
+  ]
+}