Solder cone around protruding THT leads (tent structure)

The clipped lead of a soldered THT contact protrudes
THT_LEAD_PROTRUSION_MM (1.5 mm default, 0 disables) out of the hole on
the side opposite the component, and a solder cone wraps it: full
protrusion height at the drill wall, tapering linearly to zero at the
pad edge. Painted as per-cell extra conduction-equivalent copper via
stack.thick_scale - the tall solder column at the wall pulls the joint
vicinity to lead potential (equivalent to extending the barrel wall
vertically), the taper carries the radial spreading. DC-exact additive
conductance; at f > 0 the factor multiplies the skin-corrected sheet
conductance like the via mouths (documented approximation).

The protrusion side is looked up from the owning footprint (pads store
absolute positions; component on F.Cu -> lead tents on B.Cu), with a
logged B.Cu fallback. Dump schema gains protrusion_side and
tht_protrusion_nm (defaults keep older v6 dumps loading).

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

fill_resistance/config.py

@@ -35,6 +35,11 @@ INCLUDE_TH_PADS = True          # plated through-hole pads stitch layers too;
                                 # their holes are modeled solder-filled (a
                                 # soldered component lead), so the solder core
                                 # conducts in parallel with the plating
+THT_LEAD_PROTRUSION_MM = 1.5    # clipped THT lead protrusion on the side
+                                # opposite the component: a solder cone of
+                                # this height at the drill wall (tapering to
+                                # zero at the pad edge) wraps the lead of
+                                # every soldered THT CONTACT. 0 = no cones
 SKIN_SIDES = 1                  # skin-effect field config: 1 = plane facing a
                                 # return plane (conservative), 2 = isolated foil