Replace CARTO basemaps with OpenStreetMap

[ewlarson]

Summary

• remove CARTO basemap options and API-key plumbing, with OpenStreetMap as the default across React and GeoBlacklight map viewers
• switch py-staticmaps to the canonical HTTPS OpenStreetMap provider with application identification, provider zoom limits, and new cache variants
• update diagnostics, tests, and public cache documentation, including the restriction against full-corpus priming on the public OSM tile service

Validation

• make lint-check
• python -m pytest tests/services/test_static_map_service.py (17 passed)
• npm test -- --run src/tests/basemaps.test.ts src/tests/components/resource/ResourceViewer.test.tsx (12 passed)
• affected-file ESLint check
• npm run build
• local forced one-resource static-map primer (generated 1, failed 0) and verified an 800x600 OpenStreetMap PNG

Existing repository checks

The repository-wide frontend lint and format checks remain red on pre-existing issues outside this change. The files affected by this PR pass the scoped ESLint check.