chore: 添加「毛孩子计划」品牌 logo

- 主图标 logo.svg：爱心 + 镂空爪印，暖橙渐变与 App 主色一致
- logo-lockup.svg：图标 + 中英文名称横版
- 导出 logo-512.png / logo-144.png（透明背景，小程序头像可直接用）
- options/ 保留 6 个候选方案与对比页，便于后续调整

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

pets-fe/assets/options/a-pawheart.svg

@@ -0,0 +1,12 @@
+<svg width="512" height="512" viewBox="0 0 512 512" xmlns="http://www.w3.org/2000/svg">
+<defs><linearGradient id="bgA" x1="0" y1="0" x2="0" y2="1"><stop offset="0" stop-color="#FFD08A"/><stop offset="1" stop-color="#F49A38"/></linearGradient>
+<radialGradient id="glA" cx="0.5" cy="0.28" r="0.75"><stop offset="0" stop-color="#fff" stop-opacity=".35"/><stop offset=".6" stop-color="#fff" stop-opacity="0"/></radialGradient></defs>
+<path d="M256 20 C 128 20, 20 128, 20 256 C 20 384, 128 492, 256 492 C 384 492, 492 384, 492 256 C 492 128, 384 20, 256 20 Z" fill="url(#bgA)"/>
+<path d="M256 20 C 128 20, 20 128, 20 256 C 20 384, 128 492, 256 492 C 384 492, 492 384, 492 256 C 492 128, 384 20, 256 20 Z" fill="url(#glA)"/>
+<g fill="#fff">
+<ellipse cx="138" cy="222" rx="38" ry="47" transform="rotate(-20 138 222)"/>
+<ellipse cx="214" cy="168" rx="40" ry="52" transform="rotate(-7 214 168)"/>
+<ellipse cx="298" cy="168" rx="40" ry="52" transform="rotate(7 298 168)"/>
+<ellipse cx="374" cy="222" rx="38" ry="47" transform="rotate(20 374 222)"/>
+<path d="M256 418 C190 366,148 326,148 282 C148 251,173 231,202 231 C229 231,250 249,256 271 C262 249,283 231,310 231 C339 231,364 251,364 282 C364 326,322 366,256 418 Z"/>
+</g></svg>