Model every THT pad hole: exact pad copper, lead conductor, DNP holes

- THT pad copper is now part of the conductor: the exact pad outline
  (incl. oblong/custom shapes) is fetched from KiCad once per pad and
  stamped onto every included layer (the outer shape stands in for
  inner rings). Annular rings bridge antipads, and joints land on real
  copper instead of only pour coverage.
- The internal lead conductor is modeled in every solder-filled hole:
  a cylinder of drill - THT_LEAD_CLEARANCE_MM (0.25 fab rule) with
  THT_LEAD_RHO_OHM_M (copper default; config for brass/steel leads),
  in parallel with the solder annulus and the plating.
- Drill mouths of THT pads: populated pads keep conducting mouth
  copper (stands in for the solder plug - conservative, the plug is
  worth ~200 um of copper equivalent); DNP pad holes are cut open on
  every layer like uncapped via mouths.
- Oblong pads: the coat uses the exact pad shape; the lead cone tapers
  within the inscribed circle (new pad_min_nm on ViaLink/Electrode) so
  the long axis is not overstated sideways.

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

fill_resistance/raster.py

@@ -270,11 +270,14 @@ def _paint_lead_fillets(stack: RasterStack, problem: Problem) -> None:
             y = (e.rect.y0 + e.rect.y1) / 2.0
         seen.add((int(x), int(y)))
         if e.solder and e.protrusion_side:
-            jobs.append((x, y, e.drill_nm, e.pad_nm, e.protrusion_side))
+            # oblong pads: taper to the inscribed circle (conservative)
+            jobs.append((x, y, e.drill_nm, e.pad_min_nm or e.pad_nm,
+                         e.protrusion_side))
     for v in problem.vias:
         if v.kind == "pad" and v.solder_filled and v.protrusion_side \
                 and (v.x, v.y) not in seen:
-            jobs.append((v.x, v.y, v.drill_nm, v.pad_nm, v.protrusion_side))
+            jobs.append((v.x, v.y, v.drill_nm, v.pad_min_nm or v.pad_nm,
+                         v.protrusion_side))
 
     for x, y, drill_nm, pad_nm, side in jobs:
         li = index.get(side)
@@ -333,16 +336,21 @@ def _apply_via_mouths(stack: RasterStack, problem: Problem) -> None:
     capped vias carry a cap_plating-thin copper cap over the mouth on the
     OUTER layers, uncapped vias (and inner layers either way) get an open
     hole. The fab caps only small vias: drills above cap_max_drill_nm
-    stay open even with vias_capped. Fully swallowed cells leave the
-    mask; partially covered cells keep a thickness-scaled sheet
-    conductance via stack.thick_scale."""
+    stay open even with vias_capped. THT pad mouths: populated pads are
+    solder-filled - the mouth copper stays and stands in for the plug
+    (conservative: the plug's solder is worth far more than the foil);
+    DNP pad holes are cut open on every layer. Fully swallowed cells
+    leave the mask; partially covered cells keep a thickness-scaled
+    sheet conductance via stack.thick_scale."""
     ny, nx = stack.shape2d
     h = stack.h_nm
     outer = {li for li, n in enumerate(stack.layer_names)
              if n in ("F.Cu", "B.Cu")}
     sub = (np.arange(4) + 0.5) / 4.0
     for via in problem.vias:
-        if via.kind != "via" or via.drill_nm <= 0:
+        if via.drill_nm <= 0:
+            continue
+        if via.kind == "pad" and via.solder_filled:
             continue
         r = via.drill_nm / 2.0
         j0 = max(0, math.floor((via.x - r - stack.x0_nm) / h))
@@ -362,12 +370,12 @@ def _apply_via_mouths(stack: RasterStack, problem: Problem) -> None:
         if stack.thick_scale is None:
             stack.thick_scale = np.ones(stack.masks.shape)
         for li in _via_span(problem, via):
-            if problem.vias_capped and li in outer \
+            if via.kind == "via" and problem.vias_capped and li in outer \
                     and via.drill_nm <= problem.cap_max_drill_nm:
                 ratio = min(problem.cap_plating_nm
                             / problem.layers[li].thickness_nm, 1.0)
             else:
-                ratio = 0.0
+                ratio = 0.0                 # open hole (also DNP THT holes)
             s = 1.0 - cov * (1.0 - ratio)
             gone = s <= 1e-9
             stack.masks[li, i0:i1, j0:j1] &= ~gone