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

formats/m2_coord.cpp

@@ -0,0 +1,60 @@
+#include "m2_coord.h"
+
+#include <cmath>
+#include <cstdio>
+
+namespace fmt::m2coord {
+
+std::string tile_dir(int tile_x, int tile_y) {
+    char buf[16];
+    std::snprintf(buf, sizeof(buf), "%06u", tile_id(tile_x, tile_y));
+    return buf;
+}
+
+namespace {
+Mat3 mul(const Mat3& a, const Mat3& b) {
+    Mat3 r{};
+    for (int i = 0; i < 3; ++i)
+        for (int j = 0; j < 3; ++j)
+            for (int k = 0; k < 3; ++k)
+                r.m[i * 3 + j] += a.m[i * 3 + k] * b.m[k * 3 + j];
+    return r;
+}
+Mat3 rot_x(double a) {
+    double c = std::cos(a), s = std::sin(a);
+    return {{1, 0, 0, 0, c, -s, 0, s, c}};
+}
+Mat3 rot_y(double a) {
+    double c = std::cos(a), s = std::sin(a);
+    return {{c, 0, s, 0, 1, 0, -s, 0, c}};
+}
+Mat3 rot_z(double a) {
+    double c = std::cos(a), s = std::sin(a);
+    return {{c, -s, 0, s, c, 0, 0, 0, 1}};
+}
+} // namespace
+
+Mat3 ypr_basis(double yaw_deg, double pitch_deg, double roll_deg) {
+    const double d2r = 3.14159265358979323846 / 180.0;
+    return mul(mul(rot_y(yaw_deg * d2r), rot_x(pitch_deg * d2r)), rot_z(roll_deg * d2r));
+}
+
+Mat3 object_basis_godot(double yaw_deg, double pitch_deg, double roll_deg) {
+    // Conjugate the Metin2-space rotation through the Z-up -> Y-up axis swap
+    // C = rotate(-90deg, X): (x,y,z) -> (x,z,-y).   R_godot = C * R_m2 * C^-1
+    const Mat3 C{{1, 0, 0, 0, 0, 1, 0, -1, 0}};
+    const Mat3 Ci{{1, 0, 0, 0, 0, -1, 0, 1, 0}};
+    return mul(mul(C, ypr_basis(yaw_deg, pitch_deg, roll_deg)), Ci);
+}
+
+bool parse_tile_dir(const std::string& name, int& tile_x, int& tile_y) {
+    if (name.size() != 6) return false;
+    for (char c : name)
+        if (c < '0' || c > '9') return false;
+    long id = std::strtol(name.c_str(), nullptr, 10);
+    tile_x = int(id / 1000);
+    tile_y = int(id % 1000);
+    return true;
+}
+
+} // namespace fmt::m2coord