Add CRS override fallback for projected x/y grids

[Copilot]

Projected x/y datasets without discoverable CRS metadata were falling back to regular lat/lon handling, which could render projected grids incorrectly. This change lets Gridlook use CRS supplied in the URL or catalog metadata when dataset metadata cannot provide it.

• URL and catalog CRS fallback

  • Added support for ::crs=... in hash URLs.
  • Added catalog-entry CRS lookup so a matching dataset can inherit crs from catalog metadata when no explicit URL override is present.
  • Ensured catalog-derived CRS is available before initial grid detection runs.

• Projected grid detection

  • Extended projected-grid CRS resolution to fall back in this order:
    1. dataset CRS metadata
    2. group-level projection metadata
    3. URL/catalog CRS override
  • Reused the same fallback path for grid classification and projected coordinate handling.

• Polar stereographic handling

  • Recognize common polar EPSG overrides (EPSG:3031, EPSG:3413, EPSG:3995) as polar stereographic.
  • Derive hemisphere / pole selection from override CRS when dataset metadata is missing, so polar datasets route to the curvilinear path correctly.

• Catalog-driven navigation

  • When opening/selecting datasets from a catalog, include the entry’s crs in the generated hash when available.

Example:

#https://data.source.coop/.../combined/AWI_PISM1/exp05::catalog=static/catalog.json::crs=EPSG:3031

This allows projected datasets with missing embedded CRS metadata to be classified and rendered using the intended projection instead of falling back to regular lat/lon behavior.

[eeholmes]

@copilot Still failing to fetch.

http://localhost:3000/#icechunk+https://data.source.coop/englacial/ismip6/icechunk-ais/combined/AWI_PISM1/exp05::catalog=static/catalog.json::crs=EPSG:3031::varname=acabf::projection=azimuthal_equidistant::camerastate=PYs7EoAgDAXvQo1MjCRBr-JQWFDQgB-sHO_uj3Ff93b2UHPeYok5qWEE3YCBGwJmtiwtt8QWNYGph2DXCYrXatmnEtb0ldb0FeeQLEpoRMOzX7xSyJ8X::projectionCenterLat=-90::projectionCenterLon=0::dimIndices_time=1238

[Copilot]

@copilot Still failing to fetch.

http://localhost:3000/#icechunk+https://data.source.coop/englacial/ismip6/icechunk-ais/combined/AWI_PISM1/exp05::catalog=static/catalog.json::crs=EPSG:3031::varname...

Fixed in b64482b. Icechunk URLs now skip the JSON-index fetch path, so Gridlook no longer tries to fetch() an icechunk+... URL before loading the dataset through the Zarr/Icechunk loader.