refactor: split monolithic main.c into modular source files

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

src/channel.h

@@ -0,0 +1,39 @@
+#ifndef CHANNEL_H
+#define CHANNEL_H
+
+#include <jack/jack.h>
+#include <stdatomic.h>
+
+#define LOOP_BUF_SIZE  (5 * 48000)
+#define MAX_CHANNELS   16
+
+typedef enum {
+    STATE_IDLE,
+    STATE_RECORD,
+    STATE_LOOPING,
+    STATE_PAUSED
+} looper_state;
+
+struct channel_t {
+    atomic_int    state;
+    int           prev_state;
+    float         loop_buffer[LOOP_BUF_SIZE];
+    int           loop_count;
+    int           record_pos;
+    int           playback_pos;
+    int           active;
+    jack_port_t  *audio_in;
+    jack_port_t  *audio_out;
+};
+
+/* Globals declared in looper.c */
+extern struct channel_t channels[MAX_CHANNELS];
+extern atomic_int  channel_count;
+extern int         next_channel_id;
+extern atomic_int  cmd_add;
+extern atomic_int  cmd_remove;
+
+void channel_add(jack_client_t *client, int idx);
+void channel_remove(jack_client_t *client, int idx);
+
+#endif