Add bare-minimum extension-reaper-macos REAPER extension skeleton

C/C++ extension built directly against the vendored Cockos reaper-sdk
headers (no Rust/reaper-rs wrapper layer). Loads, registers a test
action, and confirms via REAPER's console — confirmed working in
REAPER 2026-07-15.

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>

extension-reaper-macos/vendor/reaper-sdk/WDL/lice/test/Controller.mm

@@ -0,0 +1,13 @@
+#import "Controller.h"
+
+#include "main.cpp" // this would otherwise conflict in object name with main.m, which xcode made us.
+
+
+@implementation Controller
+-(void)awakeFromNib
+{
+  SWELL_RegisterCustomControlCreator(ccontrolCreator);
+  HWND h=CreateDialog(NULL,MAKEINTRESOURCE(IDD_DIALOG1),NULL,dlgProc);
+  ShowWindow(h,SW_SHOW);
+}
+@end