Mod textures, display names, and atlas injection

Mod Atlas (ModAtlas.cpp/h):
- Build merged terrain.png and items.png from mod assets (blocks/*.png, items/*.png)
- Scan vanilla atlas for empty (fully transparent) cells; place mod textures only there
- Install merged atlases over game files before Minecraft::init; restore originals after
- Hook loadUVs to create SimpleIcon objects for mod textures
- Hook registerIcon to return mod icons when requested by name
- FixupModIcons: copy field_0x48 (source-image ptr) from vanilla icons after init

Mod Strings (ModStrings.cpp/h):
- Store mod display names by description ID
- Hook GetString to serve mod names for blocks/items

API changes:
- BlockProperties/ItemProperties: .Name(displayName), namespaced .Icon()
- NativeInterop: displayName params, native_allocate_description_id, native_register_string
- Registry.Assets for string registration
- Output: mods/LegacyForge.API/, mods/ExampleMod/ (per-mod folders)

Mod discovery:
- Scan mods/*/ for mod folders; load DLLs from each
- LegacyForge.API as mod in mods/LegacyForge.API/

ExampleMod:
- Ruby ore block and ruby item with custom textures and names
- Assets: blocks/ruby_ore.png, items/ruby.png, lang files
- Furnace recipe: ruby_ore -> ruby

Runtime: loadUVs, registerIcon, getResourceAsStream, GetString hooks; stb_image for PNG

LegacyForgeRuntime/src/ModStrings.h

@@ -0,0 +1,20 @@
+#pragma once
+
+#include <unordered_map>
+#include <string>
+#include <mutex>
+
+/// <summary>
+/// Stores mod-registered display names for blocks and items.
+/// Maps description IDs (allocated from MOD_DESC_ID_BASE) to wide strings.
+/// Hooked into app.GetString() so the game displays mod names.
+/// </summary>
+namespace ModStrings
+{
+    constexpr int MOD_DESC_ID_BASE = 10000;
+
+    void Register(int descriptionId, const wchar_t* value);
+    const wchar_t* Get(int descriptionId);
+    int AllocateId();
+    bool IsModId(int id);
+}