Migrate from iOS 17 Observation to iOS 16-compatible Combine architecture.

Lower deployment target to iOS 16, replace @Observable with ObservableObject, add navigation and UI compatibility shims, and include login smoke UI tests.

Co-authored-by: Cursor <cursoragent@cursor.com>

suixinkan.xcodeproj/project.xcworkspace/xcshareddata/swiftpm/Package.resolved

@@ -1,5 +1,5 @@
 {
-  "originHash" : "40830d6592be5c997cf1b8848d6a8791afd48ce9a5e48a1f297fbae4a6de3783",
+  "originHash" : "6f02892b99a60872df0561ceead8949f780d607eccd0a776d8f299248fc13a72",
   "pins" : [
     {
       "identity" : "alibabacloud-oss-swift-sdk-v2",
@@ -19,6 +19,15 @@
         "version" : "8.10.0"
       }
     },
+    {
+      "identity" : "lottie-ios",
+      "kind" : "remoteSourceControl",
+      "location" : "https://github.com/airbnb/lottie-ios.git",
+      "state" : {
+        "revision" : "f4db77d7feacba0c2360b84a40c38a6ce8ff399d",
+        "version" : "4.6.1"
+      }
+    },
     {
       "identity" : "swift-asn1",
       "kind" : "remoteSourceControl",