Rename dataset branding to ELDOR in dataset card

Upload README.md with huggingface_hub

docs: expand class definition table with area/pixels/aliases and rename to EnIGMA

Update spatial table: remove IoU column and add foreground area (ha) per site

Revise dataset README: 14-class only, add spatial/data tables and figure section; remove Croissant section

Clarify Croissant availability and requirements for private datasets

Add dataset card with data details, split, class schema, and Croissant notes