feat: add JACK audio looper with clip state machine and tests

Co-authored-by: aider (deepseek/deepseek-coder) <aider@aider.chat>

Let's produce the blocks.makefile

@@ -0,0 +1,28 @@
+CC = gcc
+CFLAGS = -Wall -Wextra -O2 -g `pkg-config --cflags jack`
+LDFLAGS = `pkg-config --libs jack`
+TARGET = jack-looper
+SRCS = main.c engine.c
+OBJS = $(SRCS:.c=.o)
+TEST_SRCS = test_engine.c
+TEST_OBJS = $(TEST_SRCS:.c=.o)
+TEST_TARGET = test_engine
+
+.PHONY: all clean test
+
+all: $(TARGET)
+
+$(TARGET): $(OBJS)
+	$(CC) $(CFLAGS) -o $@ $^ $(LDFLAGS)
+
+%.o: %.c
+	$(CC) $(CFLAGS) -c -o $@ $<
+
+test: $(TEST_TARGET)
+	./$(TEST_TARGET)
+
+$(TEST_TARGET): $(TEST_OBJS) engine.o
+	$(CC) $(CFLAGS) -o $@ $^ $(LDFLAGS)
+
+clean:
+	rm -f $(OBJS) $(TEST_OBJS) $(TARGET) $(TEST_TARGET)