fix: sync requirements.txt with omnivoice's actual --no-deps dependencies

Pins transformers==5.3.0 (omnivoice requires exact version), restores
pydub (omnivoice dep), adds tensorboardx and webdataset.
Drops gradio (demo-only, not needed for inference).

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

requirements.txt

@@ -1,5 +1,8 @@
-transformers>=4.40.0
+transformers==5.3.0
 accelerate
 soundfile
 numpy
+pydub
+tensorboardx
+webdataset
 beautifulsoup4