chore: bump deployment target to iOS 26.0

Both devices run iPhone 17 / iOS 26. Removes availability wrappers.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

ios/Platform/Platform/ContentView.swift

@@ -238,10 +238,6 @@ struct AssistantSheetView: View {
 
 struct TabBarMinimizeModifier: ViewModifier {
     func body(content: Content) -> some View {
-        if #available(iOS 26.0, *) {
-            content.tabBarMinimizeBehavior(.onScrollDown)
-        } else {
-            content
-        }
+        content.tabBarMinimizeBehavior(.onScrollDown)
     }
 }