Tracks fence lines on the farm with type (barbed wire, high-tensile, electric, post-and-rail, woven wire, polywire, temporary), height, condition (good / fair / needs repair), last-checked date, and an auto-computed length in feet from the polyline geometry.
length_feet mirrors the acreage compute in farm_field_geo: the
WGS84 polyline is reprojected to EPSG:5070 Conus Albers Equal Area
and the geodesic length in meters is converted to US survey feet
(0.3048006096012192 m/ft). The number matches what NRCS would report
for the same fence line in a rangeland improvement filing.
Repairs-needed bubble to the top of every list and grouped kanban
because _order uses the stored rank integer contributed by
farm.rank.mixin (from farm_base), which mirrors the condition
selection through a priority map — a naive string DESC on the raw
selection would put "good" above "fair" (alpha order).
Field link is optional (ondelete="set null") so a perimeter fence
spanning multiple fields keeps its history even when one field is
archived or deleted.