Fill a panorama's border with MI-GAN: mirrored context, coarse to fine, a feathered seam

dr_pano::fill owns everything the model does not — which tiles, what
context, how to blend — behind an Inpainter trait, and dr_pano::migan is
that trait over the shipped generator on the inference engine.

The known content is mirrored across the coverage edge into the hole and
a 256-px ring, the nearest 48 px folded, so the model interpolates between
real and mirrored sky rather than extrapolating into nothing. A coarse
pass at a quarter decides the structure with the whole border in a few
tiles; fine passes in 96-px bands from the edge outward texture it; the
seam is blended over a feather inside the real edge. Every knob is a
Params field, and an Observer hears each stage for whoever is looking at
why a fill went wrong.

core/dr-pano/Cargo.toml

@@ -29,8 +29,8 @@ env_logger.workspace = true
 [features]
 default = ["xfeat", "embedded-model"]
 
-# The XFeat detector (FR-MRG-8). Off, the crate has no model and no runtime,
-# and `Detector` has no implementation — a build that only wants the geometry.
+# The XFeat detector (FR-MRG-8) and the MI-GAN filler (FR-MRG-4). Off, the
+# crate has no model and no runtime — a build that only wants the geometry.
 xfeat = ["dep:ort", "dep:dr-inference-engine", "dep:ndarray"]
 
 # Compile the weights into the binary, for the same reason `dr-segment` does: