feat(macos): port RedBox 2.0 to AppKit + finish 0.85 build bring-up

The big lift: a full native macOS port of upstream's new RedBox 2.0
error overlay (introduced in RN 0.85), plus the assorted compile fixes
needed to bring RNTester-macOS to a green build against 0.85.

## RedBox 2.0 macOS port (~1500 new lines of AppKit code)

Upstream 0.85 introduced a fullscreen "RedBox 2.0" dev error overlay
implemented as a UIKit-only UIViewController hierarchy. We need this
on macOS or the fork's dev experience regresses badly.

`RCTRedBox2Controller.mm` (+1014 lines macOS branch): full
NSViewController port. Owns a borderless NSWindow at
NSStatusWindowLevel sized to the key window. NSTableView (wrapped in
NSScrollView) renders a flat-row model derived from the iOS section
hierarchy: a RCTRedBox2RowDescriptor array with kind ∈ {Message,
CodeFrame, SectionHeader, StackFrame}. Custom NSTableCellView factory
methods for each row kind. RCTRedBox2NoSelectionRowView suppresses
highlight on non-stack rows. RCTRedBox2RootView overrides
acceptsFirstResponder + keyDown: to handle Escape / Cmd-R / Cmd-Opt-C
shortcuts. NSPasteboard.generalPasteboard for the Copy action.
NSTimer-based auto-retry countdown with Reload button title updates.
RCTRedBoxHMRClient integration unchanged (pure Foundation). Header
bar uses RCTRedBox2ErrorColor, body uses RCTRedBox2BackgroundColor,
ANSI-highlighted code frame via RCTRedBox2AnsiParser.

`RCTRedBoxController.mm` (+509 lines macOS branch): legacy
RedBoxController port (the pre-2.0 RedBox kept as fallback under
RCT_DEV_MENU). Presented via presentViewControllerAsSheet: on the key
window's content view controller (matches the pre-existing fork
pattern in RCTRedBox.mm). NSButton with keyEquivalent + Modifier mask
for Esc/Cmd-R/Cmd-Opt-C/Cmd-E shortcuts. NSButton+RCTRedBox category
mirrors UIButton+RCTRedBox for block-based handlers.

`RCTRedBox2Controller+Internal.h` and `RCTRedBoxController+Internal.h`:
gated declarations with #if !TARGET_OS_OSX/#else so consumers pick up
the right superclass + protocol set.

`RCTRedBox2AnsiParser.{h,mm}`: switched from UIColor to RCTUIColor
(fork's cross-platform NSColor alias). UIFont is left as-is since
RCTUIKitCompat.h @compatibility_alias-es it to NSFont.

`RCTRedBox.mm`: deleted ~757 lines of inline duplicate
RCTRedBoxController + UIButton/NSButton+RCTRedBox categories +
RCTRedBoxControllerActionDelegate protocol. Those are now provided by
the externalized files imported via the +Internal.h headers.

## Build bring-up fixes (other files)

- RCTUtils.mm: stray `#if !TARGET_OS_OSX` at line 42 was missing its
  inner `#endif` for the `#if !TARGET_OS_TV` nest, which silently
  swallowed lines 49-720 into the iOS branch — meaning RCTKeyWindow,
  RCTSharedApplication, RCTIsMainQueue, RCTExecuteOnMainQueue,
  RCTJSONClean, RCTJSONStringify, RCTJSONParse, RCTRoundPixelValue,
  RCTCeilPixelValue, RCTSizeInPixels, RCTScreenScale, RCTScreenSize,
  RCTViewportSize, RCTSwitchSize, RCTFontSizeMultiplier,
  RCTClassOverridesInstanceMethod, RCTJSErrorFromNSError,
  RCTJSErrorFromCodeMessageAndNSError, RCTRunningInTestEnvironment,
  RCTAreLegacyLogsEnabled, RCTUnsafeExecuteOnMainQueueSync all went
  undefined on macOS. Added the missing `#endif` and wrapped
  RCTPresentedViewController (which is iOS-only — uses
  UIWindow.rootViewController) in its own `#if !TARGET_OS_OSX`.
- RCTDevLoadingView.mm: dealloc was poking _window with iOS-only
  `.hidden`; switched to RCTPlatformWindow typedef and guarded the
  hide path with `[window orderOut:nil]` on macOS.
- RCTVirtualViewComponentView.mm: `_getParentVirtualViewContainer`
  switched UIView to RCTUIView typedef.
- RCTViewComponentView.mm: guarded `subview.accessibilityElementsHidden`
  read in RCTRecursiveAccessibilityLabel behind `#if !TARGET_OS_OSX`
  (NSView has no such property).
- RCTSurfaceTouchHandler.mm: guarded
  `otherGestureRecognizer.cancelsTouchesInView` read behind
  `#if !TARGET_OS_OSX` (NSGestureRecognizer has no such property).
- RCTScheduler.mm: CADisplayLink's
  `+displayLinkWithTarget:selector:` is iOS-only on the standalone
  class. Use the macOS 14+ `-[NSScreen displayLinkWithTarget:selector:]`
  variant.
- RCTLegacyViewManagerInteropComponentView.mm: split `hitTest:point
  withEvent:` into iOS (UIView signature) and macOS (NSView signature
  without event arg) branches.

## Validation

`xcodebuild -workspace RNTesterPods.xcworkspace -scheme RNTester-macOS
-configuration Debug -destination 'generic/platform=macOS'
ARCHS=arm64 ONLY_ACTIVE_ARCH=YES build` → `** BUILD SUCCEEDED **`.

RNTester-macOS.app: 51 MB, dylib links cleanly. Full source tree
compiles + links on macOS 14.6 target / Xcode 26.5 SDK / arm64.

Author: tvinhas

packages/react-native/React/Base/RCTUtils.mm

@@ -43,6 +43,7 @@
 // Returns the current device's orientation
 #if !TARGET_OS_TV
 UIDeviceOrientation RCTDeviceOrientation(void);
+#endif // !TARGET_OS_TV
 #endif // [macOS]
 
 // Whether the New Architecture is enabled or not
@@ -702,6 +703,7 @@ BOOL RCTRunningInAppExtension(void)
 }
 #endif
 
+#if !TARGET_OS_OSX // [macOS] RCTPresentedViewController uses iOS-only UIWindow.rootViewController + presentedViewController chain
 UIViewController *__nullable RCTPresentedViewController(void)
 {
   if ([RCTUtilsUIOverride hasPresentedViewController]) {

packages/react-native/React/CoreModules/RCTDevLoadingView.mm

@@ -68,11 +68,15 @@ - (void)dealloc
 {
   [self clearInitialMessageDelay];
   [[NSNotificationCenter defaultCenter] removeObserver:self];
-  UIWindow *window = _window;
+  RCTPlatformWindow *window = _window; // [macOS]
   _window = nil;
   if (window) {
     RCTExecuteOnMainQueue(^{
+#if !TARGET_OS_OSX // [macOS]
       window.hidden = YES;
+#else // [macOS
+      [window orderOut:nil];
+#endif // macOS]
     });
   }
 }