When the on-disk ProfilesFile is empty SkewtLive falls back to the
hrrr_profiles Postgres table, but per-QSO HrrrFetchWorker rows
sometimes land with a partial profile (4–12 levels) when individual
byte-range fetches fail. The fallback was happily picking those rows,
which rendered a stubby Skew-T missing the upper troposphere.
HrrrProfileLookup.{list_valid_times_near, read_point_near}/3 now
filter on `coalesce(cardinality(profile), 0) >= min_profile_levels`,
defaulting to 13 (HRRR's standard pressure-level set: 1000/925/850/
700/500/400/300/250/200/150/100 mb plus the two boundary surfaces).
Pass `min_profile_levels: 0` to keep the partial rows for diagnostic
queries.
Confirmed against the dev mirror: the recent table has ~3.1 M rows
at 13 levels and ~250 k at 4–12 levels; the new default skips the
partial slice cleanly.
Tests: 8/8 HrrrProfileLookupTest cases (added two new ones for the
threshold). mix credo --strict clean.