fix: skip non-FLTP audio frames in NDIReceiver

NDIlib_audio_frame_v3_t carries a FourCC. Only FLTP (float32 planar)
is handled — skip and free any other format rather than misinterpreting
compressed or integer audio bytes as floats.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

shared/NDIReceiver.hpp

@@ -172,6 +172,10 @@ public:
         }
 
         if (type == NDIlib_frame_type_audio) {
+            if (audio_frame.FourCC != NDIlib_FourCC_audio_type_FLTP) {
+                NDIlib_recv_free_audio_v3(recv_, &audio_frame);
+                return FrameKind::None;  // compressed or unknown format — skip
+            }
             audio_info.sample_rate    = audio_frame.sample_rate;
             audio_info.channels       = audio_frame.no_channels;
             audio_info.samples        = audio_frame.no_samples;