Fix iPad iOS 18 keyboard dismissal issue in search

Removed auto-focus logic that was causing keyboard show/hide loop
on iPad with docked keyboard. The keyboard was repeatedly dismissing
immediately after appearing due to interaction between keyboard
notifications, focus state changes, and view updates.

Changes:
- Removed focused state and keyboard observer from SearchModel
- Removed iOS textField reference (kept macOS only)
- Removed auto-focus logic from FocusableSearchTextField on iOS
- Cleaned up unused focus-related code

The search field now works reliably when tapped manually on iPad.
Auto-focus still works on macOS where it doesn't cause issues.

Shared/Search/FocusableSearchTextField.swift

@@ -3,27 +3,15 @@ import SwiftUI
 import SwiftUIIntrospect
 
 struct FocusableSearchTextField: View {
-    @ObservedObject private var state = SearchModel.shared
-
     var body: some View {
         SearchTextField()
         #if os(macOS)
             .introspect(.textField, on: .macOS(.v12, .v13, .v14, .v15)) { textField in
-                state.textField = textField
+                SearchModel.shared.textField = textField
             }
             .onAppear {
                 DispatchQueue.main.async {
-                    state.textField?.becomeFirstResponder()
-                }
-            }
-        #elseif os(iOS)
-            .introspect(.textField, on: .iOS(.v15, .v16, .v17, .v18)) { textField in
-                state.textField = textField
-            }
-            .onChange(of: state.focused) { newValue in
-                if newValue, let textField = state.textField, !textField.isFirstResponder {
-                    textField.becomeFirstResponder()
-                    textField.selectedTextRange = textField.textRange(from: textField.beginningOfDocument, to: textField.endOfDocument)
+                    SearchModel.shared.textField?.becomeFirstResponder()
                 }
             }
         #endif