[codex] Add DERP catalog summaries and solver hints

[cmccomb]

Summary

• Add ProblemCatalogSummary and search_problem_summaries(...) so agents can select catalog tasks without loading full briefs.
• Add OptimizationProblem.solver_hints() and expose the same payload through the optimization MCP solver_hints tool.
• Update public API docs, quickstart guidance, optimization docs, and focused tests.

Validation

• .venv/bin/python -m ruff check src/design_research_problems/__init__.py src/design_research_problems/_catalog/__init__.py src/design_research_problems/_catalog/_registry.py src/design_research_problems/problems/__init__.py src/design_research_problems/problems/_metadata.py src/design_research_problems/problems/_optimization.py tests/test_mcp_servers.py tests/test_public_api.py tests/test_registry_and_problems.py
• .venv/bin/python -m ruff format --check src/design_research_problems/__init__.py src/design_research_problems/_catalog/__init__.py src/design_research_problems/_catalog/_registry.py src/design_research_problems/problems/__init__.py src/design_research_problems/problems/_metadata.py src/design_research_problems/problems/_optimization.py tests/test_mcp_servers.py tests/test_public_api.py tests/test_registry_and_problems.py
• PYTHONPATH=src .venv/bin/python -m pytest -q tests/test_registry_and_problems.py tests/test_mcp_servers.py tests/test_public_api.py
• .venv/bin/python -m mypy src
• .venv/bin/python scripts/generate_problem_catalog_docs.py --check
• .venv/bin/python scripts/check_docs_consistency.py