refactor: replace atomic_double with fixed-point BPM and remove circular dependency

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

transport.h

@@ -45,7 +45,8 @@ typedef struct {
     atomic_uint bar_position_atomic;
     atomic_uint sample_position_atomic;
     atomic_int clock_source_atomic;    // ClockSource
-    atomic_double bpm_atomic;
+    double bpm_atomic;                 // Direct read for audio thread
+    atomic_uint bpm_atomic_raw;        // Fixed-point (BPM * 100) for frontend reads
     
     // JACK ports for MIDI clock output (when master)
     jack_port_t *midi_clock_out_port;
@@ -80,10 +81,6 @@ int transport_process(Transport *transport, jack_nframes_t nframes,
 // Reset position
 void transport_reset(Transport *transport);
 
-// Get next quantization boundary (in frames from current position)
-jack_nframes_t transport_get_next_quantize_frame(Transport *transport, 
-                                                  jack_nframes_t current_frame,
-                                                  QuantizeMode mode);
 
 // Utility
 const char* transport_state_to_string(TransportState state);