Add documentation, trained models, and examples

[taddyb]

Summary

• Documentation overhaul: Updated README, startup guide, usage docs, datasets docs, and added a config reference guide and CONTRIBUTING.md
• Trained model weights: Added v0.5.2 trained weights for both MERIT and Lynker Hydrofabric datasets with example configs and parameter map notebooks
• Project tooling: Added CLAUDE.md for AI-agent context, CLI entry point (ddr/cli.py), config docs generator script, and updated .gitignore/pyproject.toml

Test plan

• Verify documentation renders correctly on MkDocs
• Confirm example configs and notebooks run with the provided trained weights
• Check that scripts/gen_config_docs.py generates valid config reference output
• Validate CLI entry point (ddr/cli.py) works as expected

🤖 Generated with Claude Code