Barrel contacts for vias/THT pads; configurable cap-drill threshold

- Selected vias and through-hole pads inject at the drill-wall ring on
  every spanned layer (both contact models), not the whole pad face,
  so the pad/pour spreading resistance is part of the result. Vias are
  now selectable as contacts.
- Soldered THT joints: the hole is modeled solder-filled (core in
  parallel with the plating, also for stitching THT barrels) and the
  pad face carries an average-thickness solder coat over the modeled
  copper (SOLDER_THICKNESS_UM).
- Vias with drills above a configurable threshold (dialog field,
  default CAP_MAX_DRILL_MM = 0.5) keep open mouths even with capping
  selected - the fab caps only small vias.
- Geometry dump schema v6: electrode barrel fields, cap_max_drill_nm.
- Verified against R = rho/(pi t)*acosh(d/2a) for two circular contacts
  on a sheet (+2.6% at h = 0.15 mm, a = 1 mm; uniform model above the
  equipotential one as required by the contact bracket).

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

fill_resistance/dialog.py

@@ -37,6 +37,7 @@ class Selection:
     extra_cu_um: float = 0.0
     include_tracks: bool = True
     vias_capped: bool = True
+    cap_max_drill_mm: float = 0.5
     adaptive: bool = False
 
 
@@ -73,6 +74,11 @@ class _Dialog(QDialog):
         self.capped_check.setChecked(config.VIAS_CAPPED)
         form.addRow("Vias:", self.capped_check)
 
+        self.cap_drill_edit = QLineEdit(f"{config.CAP_MAX_DRILL_MM:g}")
+        self.cap_drill_edit.setEnabled(config.VIAS_CAPPED)
+        self.capped_check.toggled.connect(self.cap_drill_edit.setEnabled)
+        form.addRow("Capped up to drill [mm]:", self.cap_drill_edit)
+
         self.adaptive_check = QCheckBox(
             "adaptive cells (coarsen plane interiors; faster on large "
             "boards, corrected to ≲0.1 % of the uniform grid)")
@@ -205,6 +211,11 @@ class _Dialog(QDialog):
             extra_cu = number(self.extracu_edit, "Extra Cu")
             if extra_cu < 0:
                 raise ValueError("Extra Cu must be ≥ 0 µm.")
+        cap_max_drill = config.CAP_MAX_DRILL_MM
+        if self.capped_check.isChecked():
+            cap_max_drill = number(self.cap_drill_edit, "Capped up to drill")
+            if cap_max_drill <= 0:
+                raise ValueError("Capped-up-to drill must be > 0 mm.")
 
         def contact(box: QComboBox) -> str:
             t = box.currentText()
@@ -222,6 +233,7 @@ class _Dialog(QDialog):
                          extra_cu_um=extra_cu,
                          include_tracks=self.tracks_check.isChecked(),
                          vias_capped=self.capped_check.isChecked(),
+                         cap_max_drill_mm=cap_max_drill,
                          adaptive=self.adaptive_check.isChecked())
 
     def _try_accept(self) -> None: