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/Core/UI/RemoteImage.swift

@@ -40,7 +40,7 @@ struct RemoteImage<Placeholder: View>: View {
                 placeholder()
             }
         }
-        .onChange(of: normalizedURLString) { _, _ in
+        .onChange(of: normalizedURLString) { _ in
             didFail = false
         }
     }