Returns a data.frame listing FEBR dataset IDs that have at least
one Munsell-related column populated in their camada table,
with metadata: n_horizons, n_finite_munsell,
coverage, column_pattern.
Details
Backed by a precomputed cache shipped in
R/sysdata.rda (.FEBR_MUNSELL_INDEX; results of the
May 2026 scan over 249 datasets). On first call after install,
returns the cache instantly. Pass refresh = TRUE to
re-scan FEBR live (slow, network-dependent; updates the
in-memory copy but does not modify the bundled cache).
