fix: use atomic operations for thread-safe clip state access

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

engine.h

@@ -32,9 +32,9 @@ typedef enum {
 
 
 typedef struct {
-    ClipState state;
+    atomic_int state;          // ClipState (atomic for thread-safe access)
     float *buffer;
-    size_t buffer_size;
+    atomic_size_t buffer_size; // size_t (atomic for thread-safe access)
     size_t write_position;
     size_t read_position;
     bool is_playing;