refactor: split monolithic main.c into modular source files

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

src/channel.c

@@ -0,0 +1,38 @@
+#include <stdio.h>
+#include <string.h>
+#include <jack/jack.h>
+#include <stdatomic.h>
+#include "channel.h"
+
+void channel_add(jack_client_t *client, int idx)
+{
+    channels[idx].active = 1;
+    atomic_store(&channels[idx].state, STATE_IDLE);
+    channels[idx].prev_state = -1;
+    channels[idx].loop_count = 0;
+    channels[idx].record_pos = 0;
+    channels[idx].playback_pos = 0;
+
+    char in_name[64], out_name[64];
+    snprintf(in_name, sizeof(in_name), "channel%d_input", next_channel_id);
+    snprintf(out_name, sizeof(out_name), "channel%d_output", next_channel_id);
+
+    channels[idx].audio_in = jack_port_register(client, in_name,
+                                                JACK_DEFAULT_AUDIO_TYPE,
+                                                JackPortIsInput, 0);
+    channels[idx].audio_out = jack_port_register(client, out_name,
+                                                 JACK_DEFAULT_AUDIO_TYPE,
+                                                 JackPortIsOutput, 0);
+    if (!channels[idx].audio_in || !channels[idx].audio_out)
+        fprintf(stderr, "Failed to register ports for channel %d\n", next_channel_id);
+    next_channel_id++;
+    channel_count++;
+}
+
+void channel_remove(jack_client_t *client, int idx)
+{
+    jack_port_unregister(client, channels[idx].audio_in);
+    jack_port_unregister(client, channels[idx].audio_out);
+    channels[idx].active = 0;
+    channel_count--;
+}