Add Docker support and fix benchmark/data pipeline bugs

Containerize the application with ROCm GPU support for AMD Radeon R9700:
- Add Dockerfile with PyTorch/PyG ROCm 5.6 wheels
- Add docker-compose.yml with dashboard, live-trading, and train services
- Add .dockerignore and .env.example for configuration

Fix benchmark script to use batch_size instead of num_stocks for variable
dimensions, and replace fragile partial model surgery with a standalone MLP
for memory estimation.

Fix data pipeline to skip dates with no next trading date instead of
fabricating zero returns.

Add slippage to paper broker, optional mark-to-market prices to broker
interface, and health check endpoint for container orchestration.

.dockerignore

@@ -0,0 +1,68 @@
+# Git
+.git
+.gitignore
+
+# Python
+__pycache__
+*.py[cod]
+*$py.class
+*.so
+.Python
+build/
+develop-eggs/
+dist/
+downloads/
+eggs/
+.eggs/
+lib/
+lib64/
+parts/
+sdist/
+var/
+wheels/
+*.egg-info/
+.installed.cfg
+*.egg
+
+# Virtual environments
+venv/
+env/
+ENV/
+
+# IDE
+.vscode
+.idea
+*.swp
+*.swo
+*~
+
+# Jupyter
+.ipynb_checkpoints
+
+# OS
+.DS_Store
+Thumbs.db
+
+# Logs
+*.log
+
+# Docker
+Dockerfile
+docker-compose*.yml
+.dockerignore
+
+# Documentation
+docs/
+
+# Notebooks (heavy, usually not needed in image)
+notebooks/*.ipynb
+
+# Keep data/model directories but ignore contents
+# (they are mounted as volumes at runtime)
+data/raw/*
+data/processed/*
+data/external/*
+models/*
+
+# Don't ignore .env.example so it gets copied into image for reference
+!.env.example