calcofi_bottle — CF NetCDF releases

Versioning. Paths are named for the database release so a URL always answers "which release is this?". When a build is byte-identical to an earlier release the bytes are NOT duplicated — the release still gets a manifest and page, and the download points at the existing object. latest.txt holds the newest release.

CF scope. CF-1.10 where CF applies (coordinates, units, standard names, time). The cast -> bottle -> occurrence hierarchy uses netCDF-4 groups with explicit parent_index links; CF defines no feature type for this nesting.