darwin: add stable Xcode and iOS simulator shell (#65)

* darwin: add xcode ios simulator shell

* docs: add iOS simulator setup

shells/default.nix

@@ -2,5 +2,6 @@
   imports = [
     ./dotnix.nix
     ./android.nix
+    ./ios.nix
   ];
 }

shells/ios.nix

@@ -0,0 +1,48 @@
+_: {
+  perSystem =
+    { pkgs, ... }:
+    let
+      installIosSimulator = pkgs.writeShellApplication {
+        name = "ios-simulator-install";
+        text = ''
+          if [[ "$(/usr/bin/uname -s)" != "Darwin" ]]; then
+            echo "ios-simulator-install is only supported on macOS." >&2
+            exit 1
+          fi
+
+          xcode_app="/Applications/Xcode.app"
+          developer_dir="$xcode_app/Contents/Developer"
+
+          if [[ ! -d "$developer_dir" ]]; then
+            echo "Xcode is not installed at $xcode_app." >&2
+            echo "Apply the m2 nix-darwin configuration first." >&2
+            exit 1
+          fi
+
+          current_developer_dir="$(/usr/bin/xcode-select -p 2>/dev/null || true)"
+          if [[ "$current_developer_dir" != "$developer_dir" ]]; then
+            echo "Selecting stable Xcode..."
+            /usr/bin/sudo /usr/bin/xcode-select --switch "$developer_dir"
+          fi
+
+          echo "Installing Xcode first-launch components..."
+          /usr/bin/sudo /usr/bin/xcodebuild -runFirstLaunch
+
+          echo "Checking for newer hardware support..."
+          /usr/bin/xcodebuild -runFirstLaunch -checkForNewerComponents
+
+          echo "Downloading and installing the latest iOS Simulator runtime..."
+          /usr/bin/xcodebuild -downloadPlatform iOS
+
+          echo
+          /usr/bin/xcodebuild -version
+          /usr/bin/xcrun simctl list runtimes
+        '';
+      };
+    in
+    {
+      devShells.ios = pkgs.mkShell {
+        packages = [ installIosSimulator ];
+      };
+    };
+}