chore: Pin ML dependencies (torch, transformers, etc.) to exact local versions

requirements.txt

@@ -1,10 +1,10 @@
 # requirements.txt - v1.6
 gradio==5.49.1
-transformers>=4.50.0
-torch>=2.1.0
-accelerate>=0.33.0
-bitsandbytes>=0.43.0
-sentence-transformers>=5.0.0
+transformers==4.57.1
+torch==2.9.1
+accelerate==1.11.0
+bitsandbytes==0.48.2
+sentence-transformers==5.1.2
 pypdf>=5.0.0
 langchain-core==1.0.5
 langchain-text-splitters==1.0.0