fix: move prev_state update after MIDI clock handler to fix race condition

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

src/main.c

@@ -51,7 +51,6 @@ static int process(jack_nframes_t nframes, void *arg)
             }
             playback_pos = 0;              /* restart from beginning */
         }
-        prev_state = state;
     }
 
     /* ----- handle MIDI control port (state transitions) ----- */
@@ -160,6 +159,9 @@ static int process(jack_nframes_t nframes, void *arg)
         }
     }
 
+    /* update prev_state after all state changes */
+    prev_state = atomic_load(&current_state);
+
     return 0;
 }