Metin2 game client (P0–P11) + mobile asset pipeline

Networked client on the existing Godot 4.7 + libgr2 renderer:
- net: m2dev wire protocol (libsodium KX + XChaCha20), auth/select/game
  phases, EntityStore world model, ~all GC/CG headers. char create/delete,
  private shop / mall / cube, SHOP_GC_START_EX, guild, party (+ CG_PARTY_SET_STATE),
  quests, dragon soul, refine, safebox, exchange.
- UI: in-game windows migrated 1:1 from the reference uiscript/root .py —
  char status (/stat), inventory+equipment, select-item ([SELECT_ITEM] quest
  token), system-option + game-option + ESC system menu, private-shop 39-grid,
  party info board, shop tabs, atlas, minimap, quickbar, chat, …
- EterGrnLib polish: GR2 material blend/two-sided, LOD crossfade, motion-event
  dispatch, contact shadow, ray-AABB picking, weapon grip pre-transform.

Portable asset IO (A1) — all extension/libgr2/formats/mtproto reads routed
through godot::FileAccess (res:// PCK works on iOS/Android); standalone-lib
*_path() kept for the non-Godot CTests. AssetResolver + PropertyRegistry
switched to a baked index (bake_asset_index.gd) instead of std::filesystem.

Mobile builds: build-{android,ios}.sh, export-android.sh, pack-assets.sh,
gen-debug-keystore.sh. Assets ship as a zip mounted at runtime by
project/asset_pack.gd (adb push now; HTTP download is a drop-in later).

ctest 10/10, 34 GDScript suites, macOS/iOS/Android all build.

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_013EJxkHiNKS4kybHS3XKyAJ

extension/src/texture_util.h

@@ -0,0 +1,34 @@
+// texture_util —— 统一的「RGBA8 字节 -> ImageTexture」出口，可选 GPU 压缩。
+//
+// 桌面默认关（与旧路径逐字节一致：create_from_data + generate_mipmaps +
+// create_from_image）。移动端（OS.has_feature("mobile")）或 MTGODOT_TEXCOMP=1
+// 时，对**颜色贴图**做运行时 ASTC 8x8 压缩，省 ~6–8x 显存/带宽；编码失败自动
+// 回退 RGBA8。控制图 / 阴影图 / splat / 法线数据图不要走这个（用 RGBA8）。
+//
+// BACKLOG F4 / docs/PLATFORMS.md。
+#pragma once
+
+#include <cstddef>
+#include <cstdint>
+
+#include <godot_cpp/classes/image_texture.hpp>
+#include <godot_cpp/classes/image.hpp>
+#include <godot_cpp/classes/ref.hpp>
+
+namespace mtgodot {
+
+// 颜色贴图（sRGB 视觉内容，可压）。法线/数据图另说，暂不压。
+enum class TexUse { COLOR };
+
+// 运行时压缩开关。首次调用惰性初始化：MTGODOT_TEXCOMP 环境变量优先
+// （"1"/"0"），否则 OS.has_feature("mobile")。也可显式覆盖。
+bool texcomp_enabled();
+void texcomp_set_enabled(bool on);
+
+// w*h*4 的 level-0 RGBA8 -> ImageTexture。mipmaps=true 时先生成 mip 链
+// （ASTC 压缩前必须）。压缩仅在 texcomp_enabled() && use==COLOR 时发生。
+godot::Ref<godot::ImageTexture> make_color_texture(
+		int w, int h, const uint8_t *rgba, size_t len, bool mipmaps,
+		TexUse use = TexUse::COLOR);
+
+} // namespace mtgodot