fix: change audio models type from checkpoints to audio_models

Audio model files (MusicGen) should not be mixed with image generation
checkpoints. Changed type from 'checkpoints' to 'audio_models' to ensure
they are linked to the correct ComfyUI directory.

comfyui_models.yaml

@@ -126,7 +126,7 @@ model_categories:
       size_gb: 3
       essential: false
       category: audio
-      type: checkpoints
+      type: audio_models
       format: fp32
       vram_gb: 4
       duration_seconds: 30
@@ -137,7 +137,7 @@ model_categories:
       size_gb: 11
       essential: true
       category: audio
-      type: checkpoints
+      type: audio_models
       format: fp32
       vram_gb: 8
       duration_seconds: 30
@@ -148,7 +148,7 @@ model_categories:
       size_gb: 22
       essential: false
       category: audio
-      type: checkpoints
+      type: audio_models
       format: fp32
       vram_gb: 16
       duration_seconds: 30