Full but still broken rework of everything

native/include/video_decoder.h

@@ -87,6 +87,10 @@ int get_decoder_width();
 int get_decoder_height();
 bool is_decoder_running();
 
+// Get the shared memory base pointer (for reading frames)
+// Returns nullptr if not initialized
+uint8_t* get_shmem_base();
+
 // Write a YUV420 frame to the shared memory ring buffer
 // Called internally by the decoder thread
 // y_data, u_data, v_data: pointers to Y, U, V planes