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/asset_io.cpp

@@ -0,0 +1,40 @@
+#include "asset_io.h"
+
+#include <godot_cpp/classes/file_access.hpp>
+
+using namespace godot;
+
+namespace mtgodot {
+
+PackedByteArray read_file(const String &path) {
+	if (path.is_empty()) {
+		return PackedByteArray();
+	}
+	// FileAccess::get_file_as_bytes handles res:// / user:// / absolute OS paths.
+	return FileAccess::get_file_as_bytes(path);
+}
+
+bool file_exists(const String &path) {
+	return !path.is_empty() && FileAccess::file_exists(path);
+}
+
+Image dds_from_file(const String &path) {
+	PackedByteArray b = read_file(path);
+	if (b.is_empty()) {
+		return Image{};
+	}
+	return load_dds(b.ptr(), (size_t)b.size());
+}
+
+std::optional<gr2::File> gr2_from_file(const String &path, gr2::LoadError *err) {
+	PackedByteArray b = read_file(path);
+	if (b.is_empty()) {
+		if (err) {
+			*err = {"open", std::string("cannot read ") + path.utf8().get_data()};
+		}
+		return std::nullopt;
+	}
+	return gr2::File::load(b.ptr(), (size_t)b.size(), err);
+}
+
+} // namespace mtgodot