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/main.m

@@ -0,0 +1,14 @@
+//
+//  main.m
+//  test
+//
+//  Created by Justin Frankel on 11/9/07.
+//  Copyright __MyCompanyName__ 2007. All rights reserved.
+//
+
+#import <Cocoa/Cocoa.h>
+
+int main(int argc, char *argv[])
+{
+    return NSApplicationMain(argc,  (const char **) argv);
+}