refactor: split monolithic main.c into modular source files

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

makefile

@@ -1,9 +1,15 @@
 CC ?= gcc
-CFLAGS ?= -Wall -Wextra -g
-LDFLAGS ?= -ljack
+CFLAGS ?= -Wall -Wextra -g -Isrc
+LDFLAGS ?= -ljack -lm
 
-looper: src/main.c
-	$(CC) $(CFLAGS) -o looper src/main.c $(LDFLAGS)
+SRC = src/main.c src/looper.c src/channel.c src/midi.c
+OBJ = $(SRC:.c=.o)
+
+looper: $(OBJ)
+	$(CC) $(CFLAGS) -o $@ $^ $(LDFLAGS)
+
+src/%.o: src/%.c
+	$(CC) $(CFLAGS) -c -o $@ $<
 
 integration: looper tests/integration.c
 	$(CC) $(CFLAGS) -o integration_test tests/integration.c -ljack -lm
@@ -13,4 +19,4 @@ test: integration
 
 .PHONY: clean integration test
 clean:
-	rm -f looper integration_test
+	rm -f looper integration_test src/*.o