Add recolor pass to clean residual contamination colour

Add bgfilter/recolor.py: after despill, propagate clean neighbour chroma into
pixels whose colour is still off (residual green, or the magenta a green unmix
overshoots into), keeping luminance partway so hair texture survives. It installs
a real observed colour rather than subtracting, so it cannot overshoot. Despill
already neutralises the matte edge (off ~ 0 there), so recolor only touches the
contaminated interior and the wisps the dropout-fill rescued.

Runs as a final colour pass on the despilled foreground; pymatting + despill keep
their stronger edge handling. On the samples the magenta fringe drops sharply
(TestImage vis-magenta 0.065->0.014, TestImage2 0.085->0.031) with edge green
unchanged (vis-green ~0.02). Debug output color_mask.png replaces the despill /
foreground-background / foreground-correction maps; smoke updated.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

bgfilter/pipeline.py

@@ -15,6 +15,7 @@ from .alpha_post import (
 from .chroma import compute_bg_confidence
 from .despill import despill_green
 from .foreground import estimate_foreground_rgb
+from .recolor import recolor_foreground
 from .io import load_rgb, save_gray, save_rgb, save_rgba, write_text
 from .qa import BACKGROUND_COLORS, composite, make_qa_grid, save_previews
 from .settings import PipelineSettings
@@ -96,9 +97,12 @@ def _run_image(
     foreground = estimate_foreground_rgb(
         rgb, alpha, bg_confidence, model, settings.foreground
     )
-    corrected_rgb, despill_mask = despill_green(
+    corrected_rgb, color_mask = despill_green(
         foreground.rgb, alpha, model, settings.despill
     )
+    if settings.recolor.enabled:
+        recolored = recolor_foreground(corrected_rgb, alpha, seg_mask, settings.recolor)
+        corrected_rgb, color_mask = recolored.rgb, recolored.mask
     save_rgba(output_path, corrected_rgb, alpha)
 
     result = {
@@ -118,10 +122,8 @@ def _run_image(
         if seg_mask is not None:
             save_gray(debug / "seg_mask.png", seg_mask)
         save_gray(debug / "alpha.png", alpha)
-        save_rgb(debug / "foreground_rgb.png", foreground.rgb)
-        save_rgb(debug / "foreground_background.png", foreground.background)
-        save_gray(debug / "foreground_correction.png", foreground.correction)
-        save_gray(debug / "despill_mask.png", despill_mask)
+        save_rgb(debug / "foreground_rgb.png", corrected_rgb)
+        save_gray(debug / "color_mask.png", color_mask)
         save_previews(debug, corrected_rgb, alpha)
         tiles = {
             "input": rgb,