Include the net's traces as conductors alongside zone fills

Straight tracks become capsule outline polygons (rectangle +
semicircular caps), arc tracks annular bands with end caps, both
tessellated to the same sagitta tolerance as zone-fill arcs; they merge
into the per-layer copper next to the fills, so rasterization, via
stitching, the solver and the plots handle them unchanged. Trace-only
layers and trace-only nets now qualify as candidates. Dialog checkbox
(on by default, INCLUDE_TRACKS) toggles them per run.

Hole-less polygons (every track outline) now paint the layer mask
directly instead of allocating a full-frame temporary each.

Tests: exact N-cell chain on a rasterized capsule, analytic annular-
sector convergence for an arc trace, capsule/arc-band outline geometry
invariants, collinear-arc degradation, and fill+trace union solve.

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

fill_resistance/config.py

@@ -39,6 +39,9 @@ BUILDUP_EXTRA_CU_UM = 0.0       # optional user-added copper (busbar/wire
                                 # soldered into the opening); dialog-settable
 
 # --- Zone / layer selection ---
+INCLUDE_TRACKS = True           # the net's traces (straight + arc tracks)
+                                # conduct together with the zone fills;
+                                # dialog-toggleable
 LAYER_HINT: str | None = None   # e.g. "F.Cu" to disambiguate candidate fills
 ELECTRODE_POS_LAYER = "User.1"  # rectangles on this layer mark V+ contact parts
 ELECTRODE_NEG_LAYER = "User.2"  # rectangles on this layer mark V- contact parts