chore: trim requirements.txt to only ML pipeline deps, fix venv path, add .venv to gitignore

- requirements.txt: 230 → 11 top-level packages (removed transitive deps, CUDA/JAX/PyTorch/HuggingFace/Jupyter noise)
- CLAUDE.md: update venv setup to point at repo-root .venv
- .gitignore: add .venv/ and venv/ entries
- Memory: record venv location to avoid duplicate creation

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

CLAUDE.md

@@ -14,11 +14,10 @@ The ML pipeline lives under `Machine_Learning/`. The inference service lives und
 cd Machine_Learning
 ```
 
-Set up a Python environment:
+Activate the Python environment (already exists at repo root):
 
 ```bash
-python -m venv venv
-source venv/bin/activate
+source ../.venv/bin/activate
 pip install -r requirements.txt
 ```