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.

src/main/java/dev/zprestige/prestige/inject/TransformCache.java

@@ -1,5 +1,6 @@
 package dev.zprestige.prestige.inject;
 
+import dev.zprestige.prestige.client.AppPaths;
 import java.io.IOException;
 import java.nio.file.Files;
 import java.nio.file.Path;
@@ -31,7 +32,7 @@ final class TransformCache {
         try {
             Path jar = Path.of(Bootstrap.class.getProtectionDomain().getCodeSource().getLocation().toURI());
             if (!Files.isRegularFile(jar)) return null;
-            Path dir = Path.of(System.getProperty("java.io.tmpdir"), "PrestigeLoader", "cache");
+            Path dir = AppPaths.runtime().resolve("cache");
             Files.createDirectories(dir);
             prune(dir);
             return new TransformCache(dir, MessageDigest.getInstance("SHA-256").digest(Files.readAllBytes(jar)));