chore: remove all PrismAudio code from main branch

- Delete prismaudio_core/, data_utils/, scripts/, docs/plans/
- Delete PrismAudio nodes (feature_extractor, feature_loader, model_loader, sampler, text_only)
- Delete PrismAudio workflows (video_to_audio, text_to_audio)
- Clean nodes/utils.py: rename PRISMAUDIO_CATEGORY → SELVA_CATEGORY, remove unused helpers
- Strip PrismAudio-only deps from requirements.txt

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

nodes/selva_sampler.py

@@ -1,7 +1,7 @@
 import torch
 import comfy.utils
 
-from .utils import PRISMAUDIO_CATEGORY, get_device, get_offload_device, soft_empty_cache
+from .utils import SELVA_CATEGORY, get_device, get_offload_device, soft_empty_cache
 
 
 class SelvaSampler:
@@ -35,7 +35,7 @@ class SelvaSampler:
     RETURN_TYPES = ("AUDIO",)
     RETURN_NAMES = ("audio",)
     FUNCTION = "generate"
-    CATEGORY = PRISMAUDIO_CATEGORY
+    CATEGORY = SELVA_CATEGORY
 
     def generate(self, model, features, prompt, negative_prompt, duration, steps, cfg_strength, seed):
         from selva_core.model.flow_matching import FlowMatching