feat(ios): iCloud 同步图标替换

- icon-cloud 替换 SettingsView 中的 iCloud
- 注意：云的路径粗细与其他图标不统一，需要后续优化

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

AIStudyApp/AIStudyApp/Assets.xcassets/Icons/icon-cloud.imageset/Contents.json

@@ -0,0 +1 @@
+{"images":[{"filename":"icon-cloud.svg","idiom":"universal"}],"info":{"author":"xcode","version":1},"properties":{"template-rendering-intent":"template","preserves-vector-representation":true}}

AIStudyApp/AIStudyApp/Assets.xcassets/Icons/icon-cloud.imageset/icon-cloud.svg

@@ -0,0 +1 @@
+<svg xmlns="http://www.w3.org/2000/svg" xmlns:xlink="http://www.w3.org/1999/xlink" width="24" height="24" viewBox="0 0 24 24" fill="none"><path d="M14.7395 20C14.8201 20 14.8984 20 14.9795 20C19.3978 20 22.9795 16.4183 22.9795 12C22.9795 7.58172 19.3978 4 14.9795 4C12.4531 4 10.2057 5.17107 8.73953 7L7.51953 7C3.92968 7 1.01953 9.91015 1.01953 13.5C1.01953 17.0899 3.92968 20 7.51953 20L14.5195 20C14.5927 20 14.667 20 14.7395 20ZM16.6895 17.72C19.0397 16.9512 20.9795 14.6815 20.9795 12C20.9795 8.68629 18.2932 6 14.9795 6C11.6658 6 8.97953 8.68629 8.97953 12L6.97953 12C6.97953 10.9391 7.18452 9.92643 7.55953 9L7.51953 9C5.03425 9 3.01953 11.0147 3.01953 13.5C3.01953 15.9853 5.03425 18 7.51953 18L14.5195 18C15.0693 18 15.9023 17.9004 16.6895 17.72Z" fill-rule="evenodd" fill="#000000"></path></svg>

AIStudyApp/AIStudyApp/Features/Profile/SettingsView.swift

@@ -58,7 +58,7 @@ struct SettingsView: View {
 
                     sectionHeader("数据")
                     VStack(spacing: 0) {
-                        ZXSettingToggleRow(title: "iCloud 同步", icon: "icloud.fill", color: Color.zxTeal, isOn: $iCloudSync)
+                        ZXSettingToggleRow(title: "iCloud 同步", icon: "icon-cloud", color: Color.zxTeal, isOn: $iCloudSync)
                         ZXSettingDivider()
                         ZXSettingToggleRow(title: "自动备份", icon: "arrow.triangle.2.circlepath", color: Color.zxAccent, isOn: $autoBackup)
                     }