Fix cull mode + isolate head-collapse to a libgr2 curve bug

Rendering fixes (real):
- m2_material shaders: cull_disabled -> cull_back (inside-of-mesh faces were
  z-winning and darkening/hiding the head under the ShaderMaterial path).
- drop `* COLOR` from the shader (meshes carry no ARRAY_COLOR).

Animation: convert gr2 global poses to Godot *local* bone poses and set via
set_bone_pose (was set_bone_global_pose). MTGODOT_VERIFY=1 confirms
get_bone_global_pose(i) == conv(world[i]) for all 75 bones (<=2.6e-5).

Head/upper-armor collapse on dance_1 is NOT a Godot-route bug:
- reproduced identically in xrender-poc's bgfx demo at the same anim/t
- reproduced by the new MTGODOT_CPUSKIN=1 reference path (same LBS math as
  xrender's validated skin_mesh)
- `general/wait` / `run` render correctly in all three
=> upstream libgr2 Curve::eval (degree-2 quaternion B-spline) vs Granny.
Demo default animation switched to general/wait; documented in MIDREVIEW §4
and README. Debug scaffolding gated behind MTGODOT_VERIFY / MTGODOT_CPUSKIN.

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01WaHYEY9rwLWt21PULiYjeJ

extension/src/metin2_anim.cpp

@@ -10,6 +10,18 @@
 #include <cmath>
 #include <string>
 
+#include <godot_cpp/classes/mesh_instance3d.hpp>
+#include <godot_cpp/classes/os.hpp>
+#include <godot_cpp/classes/skin.hpp>
+
+static double _tdiff(const godot::Transform3D &a, const godot::Transform3D &b) {
+	double d = 0.0;
+	for (int r = 0; r < 3; ++r)
+		for (int c = 0; c < 3; ++c)
+			d = godot::Math::max(d, (double)godot::Math::abs(a.basis[r][c] - b.basis[r][c]));
+	return godot::Math::max(d, (double)(a.origin - b.origin).length());
+}
+
 using namespace godot;
 
 namespace mtgodot {
@@ -95,6 +107,31 @@ void Metin2AnimPlayer::reload() {
 	anim_file = std::move(f);
 	const gr2::Animation &an = anim_file->file_info().animations[0];
 	duration = an.duration;
+
+	// Diagnostic: how many anim tracks map to a model-skeleton bone by name?
+	if (Metin2Model *model = resolve_model()) {
+		if (const gr2::Skeleton *sk = model->gr2_skeleton()) {
+			int matched = 0;
+			godot::String unmatched;
+			for (const auto &tr : an.tracks) {
+				bool hit = false;
+				for (const auto &b : sk->bones) {
+					if (b.name == tr.bone_name) {
+						hit = true;
+						break;
+					}
+				}
+				if (hit) {
+					++matched;
+				} else if (unmatched.length() < 300) {
+					unmatched += String(tr.bone_name.c_str()) + " ";
+				}
+			}
+			UtilityFunctions::print(vformat(
+					"[Metin2AnimPlayer] track->bone match: %d/%d  (skel bones=%d)  unmatched: %s",
+					matched, (int)an.tracks.size(), (int)sk->bones.size(), unmatched));
+		}
+	}
 	last_info = vformat("anim '%s' dur=%.3f tracks=%d anims=%d",
 			String(an.name.c_str()), duration, (int)an.tracks.size(),
 			(int)anim_file->file_info().animations.size());
@@ -127,9 +164,43 @@ void Metin2AnimPlayer::apply_pose(double t) {
 
 	gr2::sample_pose(*sk, an, (float)tt, world_buf, skin_buf);
 
-	const int n = (int)std::min<size_t>(world_buf.size(), (size_t)skel->get_bone_count());
+	if (godot::OS::get_singleton()->get_environment("MTGODOT_CPUSKIN") == "1") {
+		model->enable_cpu_skin(true);
+		model->cpu_skin(skin_buf);
+		return;
+	}
+
+	// Convert gr2 global poses -> Godot *local* bone poses and set those.
+	// (Setting global poses directly hits a parent-ordering hazard in
+	// Skeleton3D::set_bone_global_pose that detaches head/upper-body meshes
+	// once bones leave the bind pose.)
+	const int n = (int)std::min<size_t>(world_buf.size(),
+			std::min<size_t>(sk->bones.size(), (size_t)skel->get_bone_count()));
 	for (int i = 0; i < n; ++i) {
-		skel->set_bone_global_pose(i, gr2_to_godot(world_buf[i]));
+		const godot::Transform3D t_i = gr2_to_godot(world_buf[i]);
+		const int parent = sk->bones[i].parent;
+		if (parent < 0 || parent >= n) {
+			skel->set_bone_pose(i, t_i);
+		} else {
+			skel->set_bone_pose(i, gr2_to_godot(world_buf[parent]).affine_inverse() * t_i);
+		}
+	}
+
+	if (!verified_ && OS::get_singleton()->get_environment("MTGODOT_VERIFY") == "1") {
+		verified_ = true;
+		skel->force_update_all_bone_transforms();
+		double d_pose = 0.0;
+		int w_pose = -1;
+		for (int i = 0; i < n; ++i) {
+			double dp = _tdiff(skel->get_bone_global_pose(i), gr2_to_godot(world_buf[i]));
+			if (dp > d_pose) {
+				d_pose = dp;
+				w_pose = i;
+			}
+		}
+		UtilityFunctions::print(vformat(
+				"[Metin2AnimPlayer] verify: max |global_pose - conv(world)| = %.6f @ bone %d '%s'",
+				d_pose, w_pose, w_pose >= 0 ? String(sk->bones[w_pose].name.c_str()) : String()));
 	}
 }