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

ExampleMod/assets/lang/de-DE.lang

@@ -0,0 +1,5 @@
+# ExampleMod language file (de-DE)
+# German translations for ExampleMod content.
+
+block.examplemod.ruby_ore=Rubinerz
+item.examplemod.ruby=Rubin

ExampleMod/assets/lang/en-GB.lang

@@ -0,0 +1,7 @@
+# ExampleMod language file (en-GB)
+# Display names for blocks and items.
+# In the current API, use BlockProperties.Name() and ItemProperties.Name() instead.
+# This file documents the expected format for future multi-locale support.
+
+block.examplemod.ruby_ore=Ruby Ore
+item.examplemod.ruby=Ruby