feat(ios): App 图标替换为知习 Logo

- 从 startup-plan/图片资源/logo.png 复制到 AppIcon.appiconset
- 1254×1254，Xcode 自动生成所需尺寸

Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>

AIStudyApp/AIStudyApp/Assets.xcassets/AppIcon.appiconset/Contents.json

@@ -1,6 +1,7 @@
 {
   "images" : [
     {
+      "filename" : "logo.png",
       "idiom" : "universal",
       "platform" : "ios",
       "size" : "1024x1024"
@@ -12,6 +13,7 @@
           "value" : "dark"
         }
       ],
+      "filename" : "logo.png",
       "idiom" : "universal",
       "platform" : "ios",
       "size" : "1024x1024"
@@ -23,6 +25,7 @@
           "value" : "tinted"
         }
       ],
+      "filename" : "logo.png",
       "idiom" : "universal",
       "platform" : "ios",
       "size" : "1024x1024"