M2.5: ShaderMaterial + texture resolution + fog; multi-skeleton verified

- m2_material: Metin2-style ShaderMaterial. blend_mix shader (opaque /
  alpha-blend / alpha-test-cutout via `mode` uniform) + blend_add shader
  (additive glow). modulate(tex, COORD) * COLOR, diffuse_lambert.
- Metin2Model: material_mode prop ("metin2" ShaderMaterial | "standard");
  _resolve_texture does filename-convention + case-insensitive dir scan of
  *.dds (face/hair keyword slots, stem match, fallback); set_surface_texture
  override; guess_blend heuristic (hair->cutout, cape->alpha, effect->add).
  Texture cache. Fixed opaque path to NOT alpha-discard (was hiding bodies).
- harness: AABB-based camera framing, engine depth fog (MTGODOT_FOG=1),
  MTGODOT_ANIM_T fixed-pose capture (needs explicit anim reload first),
  MTGODOT_AUTOSHOT batch screenshot.

Verified: warrior 5/5 surfaces textured under the shader (t=9 dance pose,
lit, fogged). assassin 17/17 textured via dir scan. shaman_lord (gr2 v7)
renders. Screenshots test/golden/m25-*.png, m2c-t*.png.

Gap (M2.5 gate not closed): libgr2 POD API exposes no material/texture-name/
blend data, so multi-slot -> texture/blend mapping is heuristic only. Needs
a libgr2 material API (gr2_material.cpp walking the type tree) — same gap as
xrender-poc M1 T5. Documented in docs/GODOT-POC-PLAN.md §M2.5 T2.5.6.

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

extension/src/m2_material.cpp

@@ -0,0 +1,95 @@
+#include "m2_material.h"
+
+#include <godot_cpp/classes/shader.hpp>
+#include <godot_cpp/classes/shader_material.hpp>
+#include <godot_cpp/classes/texture2d.hpp>
+#include <godot_cpp/variant/color.hpp>
+
+using namespace godot;
+
+namespace mtgodot {
+namespace {
+
+// blend_mix shader: covers opaque (mode 0, alpha-scissor) and alpha (mode 1).
+const char *SRC_MIX = R"(shader_type spatial;
+render_mode blend_mix, depth_draw_opaque, cull_disabled, diffuse_lambert, specular_disabled;
+
+uniform sampler2D albedo_tex : source_color, filter_linear_mipmap, repeat_enable;
+uniform bool use_texture = true;
+uniform vec4 modulate : source_color = vec4(1.0);
+uniform float alpha_scissor : hint_range(0.0, 1.0) = 0.5;
+uniform int mode = 0; // 0 opaque | 1 alpha-blend | 2 alpha-test (cutout)
+
+void fragment() {
+	vec4 c = use_texture ? texture(albedo_tex, UV) : vec4(1.0);
+	c *= modulate * COLOR;
+	if (mode == 2 && c.a < alpha_scissor) {
+		discard;
+	}
+	ALBEDO = c.rgb;
+	ALPHA = (mode == 1) ? c.a : 1.0;
+}
+)";
+
+// blend_add shader: additive glow (effects, enchant overlays).
+const char *SRC_ADD = R"(shader_type spatial;
+render_mode blend_add, depth_draw_opaque, depth_test_disabled, cull_disabled, unshaded;
+
+uniform sampler2D albedo_tex : source_color, filter_linear_mipmap, repeat_enable;
+uniform bool use_texture = true;
+uniform vec4 modulate : source_color = vec4(1.0);
+
+void fragment() {
+	vec4 c = use_texture ? texture(albedo_tex, UV) : vec4(1.0);
+	c *= modulate * COLOR;
+	ALBEDO = c.rgb * c.a;
+	ALPHA = 1.0;
+}
+)";
+
+Ref<Shader> shader_for(bool additive) {
+	static Ref<Shader> s_mix;
+	static Ref<Shader> s_add;
+	Ref<Shader> &slot = additive ? s_add : s_mix;
+	if (slot.is_null()) {
+		slot.instantiate();
+		slot->set_code(additive ? SRC_ADD : SRC_MIX);
+	}
+	return slot;
+}
+
+} // namespace
+
+Ref<ShaderMaterial> make_material(const MaterialDesc &d) {
+	Ref<ShaderMaterial> m;
+	m.instantiate();
+
+	const bool additive = (d.blend == BlendMode::Add);
+	m->set_shader(shader_for(additive));
+
+	const bool has_tex = d.albedo.is_valid();
+	m->set_shader_parameter("use_texture", has_tex);
+	if (has_tex) {
+		m->set_shader_parameter("albedo_tex", d.albedo);
+	}
+	m->set_shader_parameter("modulate", has_tex ? Color(1, 1, 1, 1) : Color(0.8, 0.8, 0.82, 1));
+
+	if (!additive) {
+		m->set_shader_parameter("alpha_scissor", d.alpha_scissor);
+		int mode = 0;
+		if (d.blend == BlendMode::Alpha) {
+			mode = 1;
+		} else if (d.blend == BlendMode::AlphaTest) {
+			mode = 2;
+		}
+		m->set_shader_parameter("mode", mode);
+	}
+	if (d.blend == BlendMode::Alpha) {
+		m->set_render_priority(1);
+	} else if (additive) {
+		m->set_render_priority(2);
+	}
+	return m;
+}
+
+} // namespace mtgodot