Build offline OpenPrestige release bundles

Rename the injector and package it with an embedded payload for Windows, Linux, and macOS x64/ARM64. Add a core-only ImGui native build, multi-platform CI and release packaging, and shared per-user storage with legacy config migration.

scripts/imgui-core/GenerateCore.java

@@ -0,0 +1,8 @@
+import com.badlogic.gdx.jnigen.NativeCodeGenerator;
+
+public final class GenerateCore {
+    public static void main(String[] args) throws Exception {
+        new NativeCodeGenerator().generate(args[0], args[1], args[2], null,
+                new String[] {"**/extension/**", "**/lwjgl3/**"});
+    }
+}