- Add polar stereographic coordinate transform (EPSG:3413/3031) in geo.py
so geographic bboxes are properly converted to projected meters
- Auto-detect image format: PNG for colormapped layers (preserves exact
colors for query_point reverse-mapping), JPEG for true-color
- get_imagery format parameter now defaults to "auto" instead of "jpeg"
- Embed NDVI seasonal timelapse and polar stereo images in README
- 96 tests passing
