feat(character): ComfyUI blueprints and a render-vs-blueprint evaluation

Two tools that turn character work into something measurable.

- Tools/comfyui_character_blueprint.py generates a four-view sheet (front, side, back,
  head) plus a contact sheet from one description, with fixed seeds and a JSON record
  of prompts and prompt ids. First sheet: 'GigLine walker', lean pedestrian in a navy
  tee, jeans and sneakers.
- Tools/character_match.py compares a rendered character against a sheet: figure
  aspect, fill and coverage deltas, mean CIE76 colour distance, dominant-palette
  distance, and a side-by-side montage. The deltas stay separate on purpose - a single
  similarity score between a photoreal sheet and a low-detail body would be a number
  with no meaning.
- comfyui_generate.py grew wait_for_image() so both tools share the polling path
  instead of duplicating it.
- 13 unit tests for the colour maths, masks and palette; 95 tool tests pass.

First real result, recorded rather than smoothed over: aspect delta 1.24, fill delta
0.12, mean deltaE 31.9, palette deltaE 25.4. The montage shows the reason - the model
is a nude body and the blueprint wears a tee and jeans, so clothing dominates every
metric. Figure segmentation is explicit (--render-box): auto-detection picked backdrop
blobs on every attempt, and a background plate is the proper fix.

Game/GigLine/Source/GigLine/GigLineCharacter.cpp

@@ -92,6 +92,17 @@ AGigLineCharacter::AGigLineCharacter()
 
 	// Hair: a separate component that copies the body's pose, so it follows the head
 	// bone without a second rig or a second animation. Hidden with the body.
+	// The skin material is assigned at runtime: a SkeletalMesh slot cannot be repointed
+	// from Python, so Tools/ue_character_materials.py builds M_Character_Skin and the
+	// pawn binds it here. Without this the imported FBX phong material is used and the
+	// generated pore detail never reaches the render.
+	static ConstructorHelpers::FObjectFinder<UMaterialInterface> SkinMaterialFinder(
+		TEXT("/Game/Test/Character/M_Character_Skin.M_Character_Skin"));
+	if (SkinMaterialFinder.Succeeded())
+	{
+		GetMesh()->SetMaterial(0, SkinMaterialFinder.Object);
+	}
+
 	HairMesh = CreateDefaultSubobject<USkeletalMeshComponent>(TEXT("HairMesh"));
 	HairMesh->SetupAttachment(GetCapsuleComponent());
 	HairMesh->SetCollisionEnabled(ECollisionEnabled::NoCollision);