ui: 骨架屏替代全部页面级加载 spinner

- 新增 Skeleton 组件库：Skeleton、SkeletonCircle 基础元素 + 5 个业务骨架
  （SwipeDeck、ProfileCard、RecordItem、BlindboxRoom、BlindboxList、RoomCard）
- 替换 room、profile、blindbox 列表、blindbox 房间、invite 5 个页面的加载态
- 替换 profile 历史记录 / 收藏列表的内联加载 spinner
- 更新 project-conventions.mdc：新增 Loading States 规范，
  要求页面级和列表级加载必须使用骨架屏

src/app/profile/page.tsx

@@ -25,6 +25,7 @@ import {
 } from "lucide-react";
 import EmptyState from "@/components/EmptyState";
 import RestaurantImage from "@/components/RestaurantImage";
+import { ProfileCardSkeleton, RecordItemSkeleton } from "@/components/Skeleton";
 import { getUserId, getCachedProfile, setCachedProfile, setCachedPreferences, logout } from "@/lib/userId";
 import { getAvatarBg, AVATARS } from "@/lib/avatars";
 import type { UserProfile, UserPreferences, DecisionRecord, FavoriteRecord, Restaurant } from "@/types";
@@ -256,8 +257,26 @@ export default function ProfilePage() {
 
   if (loading) {
     return (
-      <div className="flex min-h-dvh items-center justify-center bg-background">
-        <Loader2 size={24} className="animate-spin text-muted" />
+      <div className="h-dvh bg-background pb-16 overflow-y-auto scrollbar-none">
+        <nav className="sticky top-0 z-10 flex h-14 items-center gap-3 bg-background/80 px-4 backdrop-blur-sm">
+          <div className="h-8 w-8" />
+          <h1 className="flex-1 text-base font-bold text-white">个人中心</h1>
+        </nav>
+        <div className="mx-auto max-w-sm px-5">
+          <ProfileCardSkeleton />
+          <div className="mt-4 rounded-2xl bg-surface p-4 ring-1 ring-border">
+            <div className="flex flex-col gap-2">
+              <RecordItemSkeleton />
+              <RecordItemSkeleton />
+            </div>
+          </div>
+          <div className="mt-4 rounded-2xl bg-surface p-4 ring-1 ring-border">
+            <div className="flex flex-col gap-2">
+              <RecordItemSkeleton />
+              <RecordItemSkeleton />
+            </div>
+          </div>
+        </div>
       </div>
     );
   }
@@ -534,8 +553,9 @@ export default function ProfilePage() {
                 className="overflow-hidden"
               >
                 {historyLoading ? (
-                  <div className="flex justify-center py-6">
-                    <Loader2 size={18} className="animate-spin text-muted" />
+                  <div className="mt-3 flex flex-col gap-2">
+                    <RecordItemSkeleton />
+                    <RecordItemSkeleton />
                   </div>
                 ) : history.length === 0 ? (
                   <EmptyState
@@ -616,8 +636,9 @@ export default function ProfilePage() {
                 className="overflow-hidden"
               >
                 {favLoading ? (
-                  <div className="flex justify-center py-6">
-                    <Loader2 size={18} className="animate-spin text-muted" />
+                  <div className="mt-3 flex flex-col gap-2">
+                    <RecordItemSkeleton />
+                    <RecordItemSkeleton />
                   </div>
                 ) : favorites.length === 0 ? (
                   <EmptyState