fix: Pin exact dependency versions for stable builds

**Dependency Version Pinning:**
- gradio==5.9.1 (from >=5.0.0)
- transformers==4.46.0 (from >=4.30.0)
- torch==2.5.1 (from >=2.0.0)
- safetensors==0.4.5 (from >=0.4.0)
- accelerate==1.2.1 (from >=0.20.0)

**Benefits:**
- Reproducible builds on HF Spaces
- Avoid version conflicts during Docker image build
- Prevent unexpected breaking changes from newer versions
- Reduce build time by avoiding version resolution

**Fixes:**
- Resolves 400 Bad Request error during Docker push
- Ensures consistent behavior across deployments
- Matches README.md sdk_version specification

🤖 Generated with [Claude Code](https://claude.com/claude-code)

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

requirements.txt

@@ -1,5 +1,5 @@
-gradio>=5.0.0
-transformers>=4.30.0
-torch>=2.0.0
-safetensors>=0.4.0
-accelerate>=0.20.0
+gradio==5.9.1
+transformers==4.46.0
+torch==2.5.1
+safetensors==0.4.5
+accelerate==1.2.1