stacr 0.1.0

• Initial CRAN submission.
• Core functions: stac_search(), stac_collections(), stac_items(), stac_download(), stac_catalogs().
• All results returned as tibbles (never nested lists).
• Catalog registry with Planetary Computer, Earth Search, and USGS endpoints.
• stac_to_cube() bridge to ‘gdalcubes’ for raster data cube analysis.
• stac_map() interactive leaflet mapping of item footprints.
• stac_search_raw() for raw rstac results (input to stac_download() and stac_to_cube()).