Wire the adaptive quadtree grid into the solve path (phase 2)

config.ADAPTIVE_CELLS (dialog checkbox "adaptive cells", off by
default; standalone --adaptive) routes run_solve through
fill_resistance/adaptive.py: per-layer balanced leaf grids where every
non-uniform fine cell (electrodes, 1D chain cells, buildup, via-mouth
thickness map) is pinned at the fine size, leaf faces via the
series-half-cell rule, chain links and barrels re-attached by node id,
connectivity restriction and both contact models on the leaf graph via
solver cores extracted for reuse (_equipotential_core, _uniform_core,
_conductance_params, _barrel_links). All fields (V, |J|, power density)
are computed per leaf and expanded to the fine grid, so plots, summary
and dumps are unchanged.

Element sizes: minimum = the grid cell size itself (auto / dialog /
CELL_UM_OVERRIDE); maximum = ADAPTIVE_MAX_CELL_UM (2 mm default);
ADAPTIVE_GUARD sets the clearance a block needs to grow.

Measured end-to-end (feature-dense 120x120 plate, h=50um): 25.9 s ->
5.4 s, 5.58M -> 823k unknowns, R -1.1%. Accuracy documented honestly:
coarse-fine interfaces carry a first-order tangential flux error
biasing R low by ~0.5-2% depending on geometry (worst on narrow
strips); the earlier assumption that linear fields solve exactly on the
leaf graph was wrong - offset centers across size transitions leave an
unpaired residue. Gradient-corrected interface fluxes remain as phase 4
if tighter accuracy per leaf is needed.

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
+    adaptive: bool = False
 
 
 class _Dialog(QDialog):
@@ -72,6 +73,12 @@ class _Dialog(QDialog):
         self.capped_check.setChecked(config.VIAS_CAPPED)
         form.addRow("Vias:", self.capped_check)
 
+        self.adaptive_check = QCheckBox(
+            "adaptive cells (coarsen plane interiors; faster on large "
+            "boards, ~0.5–2 % low bias)")
+        self.adaptive_check.setChecked(config.ADAPTIVE_CELLS)
+        form.addRow("Grid:", self.adaptive_check)
+
         self.contact1_box = QComboBox()
         self.contact2_box = QComboBox()
         form.addRow(f"V+ ({e1_label}):", self.contact1_box)
@@ -214,7 +221,8 @@ class _Dialog(QDialog):
                          include_buildup=self.buildup_check.isChecked(),
                          extra_cu_um=extra_cu,
                          include_tracks=self.tracks_check.isChecked(),
-                         vias_capped=self.capped_check.isChecked())
+                         vias_capped=self.capped_check.isChecked(),
+                         adaptive=self.adaptive_check.isChecked())
 
     def _try_accept(self) -> None:
         try: