Replace file overwrite with CreateFileW hook for mod texture loading

Instead of backing up and overwriting vanilla terrain.png/items.png,
hook CreateFileW to redirect file opens to merged atlases in
mods/ModLoader/generated/. The hook is active only during init and
removed once textures are loaded into GPU memory. Vanilla game files
are never modified.

WeaveLoaderRuntime/src/GameHooks.cpp

@@ -157,12 +157,15 @@ namespace GameHooks
         ModAtlas::BuildAtlases(base + "mods", gameResPath);
     atlas_done:
 
-        // Overwrite the game's atlas PNGs with our merged versions BEFORE init
-        // loads them. The originals are backed up and restored after init.
-        ModAtlas::InstallAtlasFiles(gameResPath);
+        // Redirect terrain.png/items.png file opens to our merged atlases
+        // so the game loads mod textures without modifying vanilla files.
+        ModAtlas::InstallCreateFileHook(gameResPath);
 
         Original_MinecraftInit(thisPtr);
 
+        // Textures are loaded into GPU memory now; remove the redirect.
+        ModAtlas::RemoveCreateFileHook();
+
         // After init, vanilla icons have their source-image pointer (field_0x48)
         // fully populated. Copy it to our mod icons so getSourceHeight() works.
         ModAtlas::FixupModIcons();