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

project/asset_root.gd

@@ -0,0 +1,47 @@
+# AssetRoot —— Metin2 资源根目录的唯一解析点。
+#
+# 资源（`.gr2` / `.dds` / `locale` / `OutdoorA1` / `uiscript` …）不进版本库。
+# 解析顺序：
+#   1. 环境变量 MT_ASSETS（绝对路径）
+#   2. res://../assets            —— 开发树（仓库根的 assets/）
+#   3. <可执行文件>/../Resources/assets  —— 打包进 .app 内
+#   4. <.app 同级>/assets         —— .app 旁边放一份
+# 都没有就返回 res://../assets（调用方自行 warn）。
+#
+#   var root := AssetRoot.path()
+#   var il   := AssetRoot.sub("locale/locale/common/item_list.txt")
+#   if AssetRoot.available(): ...
+class_name AssetRoot
+extends RefCounted
+
+static func _candidates() -> Array:
+	var out: Array = []
+	var env := OS.get_environment("MT_ASSETS")
+	if env != "":
+		out.append(env)
+	# 挂载的 assets.zip（AssetPack）把资源放到 res://assets —— 移动端主路径。
+	# 用 asset_index.txt 作为「pack 已挂载」信号（空的 project/assets/ 占位目录不算）。
+	if FileAccess.file_exists("res://assets/asset_index.txt"):
+		out.append("res://assets")
+	out.append(ProjectSettings.globalize_path("res://../assets"))
+	var exe := OS.get_executable_path()
+	if exe != "":
+		var exe_dir := exe.get_base_dir()                       # .../mtgodot-poc.app/Contents/MacOS
+		out.append(exe_dir.path_join("../Resources/assets").simplify_path())
+		out.append(exe_dir.path_join("../../../assets").simplify_path())  # 与 .app 同级
+		out.append(exe_dir.path_join("assets"))                 # 与裸可执行文件同级
+	return out
+
+static func path() -> String:
+	for c in _candidates():
+		if DirAccess.dir_exists_absolute(c):
+			return c
+	return ProjectSettings.globalize_path("res://../assets")
+
+# 资源根下的子路径（用 path_join，跨平台）。
+static func sub(rel: String) -> String:
+	return path().path_join(rel)
+
+# 资源目录是否真的存在（缺资源的测试据此跳过）。
+static func available() -> bool:
+	return DirAccess.dir_exists_absolute(path())