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/jnetlib/Makefile

@@ -0,0 +1,20 @@
+# freebsd3 makefile
+default: jnl.a
+
+LDFLAGS = -pthread 
+CFLAGS = -s -O2 -Wall -DTHREAD_SAFE -D_THREAD_SAFE -D_REENTRANT
+CC = gcc
+CPP = g++
+CXX = g++
+
+OBJS = asyncdns.o connection.o httpget.o httpserv.o listen.o util.o sercon.o
+
+jnl.a: ${OBJS}
+	-rm -f jnl.a
+	ar rcs jnl.a ${OBJS}
+
+test: ${OBJS} test.o
+	$(CC) ${CFLAGS} -o test test.o ${OBJS} ${LDFLAGS}
+
+clean:
+	-rm -f ${OBJS} test jnl.a test.o