feat: add NASA PSI agent tools (psi_api_tool + metadata_expansion_tool)

[maf404]

Summary

Adds two tools under akd_ext/tools/psi/ for NASA's Physical Sciences Informatics (PSI) data repository, following the BaseTool / @mcp_tool pattern. All PSI endpoints are public — no API key required.

• psi_api_tool — one tool with an operation selector: discover_investigations, get_investigation, search_files, navigate_dataset, retrieve_file, and lookup_publication (DataCite).
• metadata_expansion_tool — enriches, caches, and ranks investigation metadata for candidate selection.

This mirrors the reference psi-agent-tools design (one API tool + one metadata tool) rather than one tool per operation.

Notes

• Async (httpx.AsyncClient); httpx is already a transitive dependency, so nothing new is added.
• Errors raise typed exceptions (akd-ext idiom). Results are summarized by default; response_mode="raw"/"both" also returns the raw upstream JSON.
• All endpoints and paths are config fields with env-var defaults, so both tools construct zero-arg.

Testing

uv run pytest -m "not integration" tests/tools/psi/   # 24 offline (httpx.MockTransport, no network)
uv run pytest -m integration tests/tools/psi/         # 7 live (PSI + DataCite)
uv run pre-commit run --all-files                     # ruff clean