feat(fe): 冷启动过渡动画 — 爪印一步步踩上屏幕 + 收尾渐隐

- 启动登录已在 app.js onLaunch + store.ready 单例里最早触发，进首页不再等登录
- 闪屏把原来的单个 logo 换成左右交替的爪印小径，逐个延迟「踩」上屏走向 logo
- 登录/拉宠物完成后：先保证闪屏至少 900ms 让爪印走几步，再整屏渐隐放大切走，
  不再硬切到首页/建档向导

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>

pets-fe/pages/onboarding/onboarding.wxss

@@ -16,18 +16,35 @@
   background:
     radial-gradient(circle at 50% 32%, rgba(253,179,92,.28), transparent 55%),
     var(--bg);
+  transition:opacity .34s ease, transform .34s ease;
 }
-.boot-badge{
-  width:184rpx;height:184rpx;border-radius:44rpx;
-  background:linear-gradient(150deg,#FFB865,#F5943E);
-  display:flex;align-items:center;justify-content:center;
-  box-shadow:0 18rpx 42rpx rgba(214,138,52,.4);
-  animation:boot-pop .5s ease both, boot-breathe 2.4s ease-in-out .5s infinite;
-}
-.boot-name{margin-top:var(--sp-5);font-size:var(--fs-2xl);font-weight:var(--fw-b);letter-spacing:-1rpx}
+/* 收尾渐隐：整屏淡出 + 轻微放大，像走进 App，而不是硬切 */
+.boot--out{opacity:0;transform:scale(1.06);pointer-events:none}
+
+/* 爪印小径：一串爪印从下往上、左右交替地一步步踩出来，走向 logo */
+.paw-trail{position:relative;width:320rpx;height:540rpx;margin:0 auto}
+.paw-trail .pw{position:absolute;animation:paw-step 2.4s ease-in-out infinite both}
+.paw-trail .paw{width:100rpx;height:92rpx}
+.paw-trail .foot-l{transform:rotate(-13deg) scale(.6)}
+.paw-trail .foot-r{transform:rotate(13deg) scale(-.6,.6)} /* 负 X 缩放 = 镜像成另一只脚 */
+/* 之字形落点（bottom 越大越靠上）+ 逐个延迟，形成「一步步走」 */
+.paw-trail .pw-0{left:96rpx;bottom:0;animation-delay:0s}
+.paw-trail .pw-1{left:184rpx;bottom:96rpx;animation-delay:.2s}
+.paw-trail .pw-2{left:96rpx;bottom:192rpx;animation-delay:.4s}
+.paw-trail .pw-3{left:184rpx;bottom:288rpx;animation-delay:.6s}
+.paw-trail .pw-4{left:96rpx;bottom:384rpx;animation-delay:.8s}
+.paw-trail .pw-5{left:184rpx;bottom:480rpx;animation-delay:1s}
+
+.boot-name{margin-top:var(--sp-4);font-size:var(--fs-2xl);font-weight:var(--fw-b);letter-spacing:-1rpx}
 .boot-tip{margin-top:var(--sp-2);color:var(--muted);font-size:var(--fs-md)}
-@keyframes boot-pop{from{opacity:0;transform:scale(.8)}to{opacity:1;transform:scale(1)}}
-@keyframes boot-breathe{0%,100%{transform:translateY(0)}50%{transform:translateY(-10rpx)}}
+/* 每个爪印：从上方一点、缩着落下 → 踩实（轻微过冲）→ 停一下 → 淡出，循环 */
+@keyframes paw-step{
+  0%{opacity:0;transform:translateY(-14rpx) scale(.7)}
+  10%{opacity:1;transform:translateY(0) scale(1.12)}
+  20%{opacity:1;transform:translateY(0) scale(1)}
+  68%{opacity:1;transform:translateY(0) scale(1)}
+  86%,100%{opacity:0;transform:translateY(0) scale(1)}
+}
 
 .hero{text-align:center;padding:60rpx 0 var(--sp-5)}
 .pet-logo{