feat: replace mutex with lock-free ring buffer for real-time audio recording

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

dispatcher.h

@@ -109,6 +109,12 @@ typedef struct {
         int current_batch_size;              // NEW: current batch being recorded
     } undo;
     
+    // Ring buffers for real-time recording (written by JACK callback, read by dispatcher)
+    // Lock-free: single producer (JACK callback), single consumer (dispatcher thread)
+    float record_buffer[MAX_CHANNELS][MAX_BUFFER_SIZE];
+    atomic_size_t record_write_pos[MAX_CHANNELS];  // Only written by JACK callback
+    atomic_size_t record_read_pos[MAX_CHANNELS];   // Only written by dispatcher thread
+    
     // Carla host
     CarlaHost carla_host;