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.

injector/crates/paths.rs

@@ -0,0 +1,36 @@
+use std::io;
+use std::path::PathBuf;
+
+fn env_path(name: &str) -> Option<PathBuf> {
+    std::env::var_os(name)
+        .filter(|path| !path.is_empty())
+        .map(PathBuf::from)
+}
+
+pub fn root() -> PathBuf {
+    #[cfg(windows)]
+    let base = env_path("APPDATA")
+        .or_else(|| env_path("USERPROFILE").map(|home| home.join("AppData/Roaming")));
+    #[cfg(target_os = "macos")]
+    let base = env_path("HOME").map(|home| home.join("Library/Application Support"));
+    #[cfg(all(unix, not(target_os = "macos")))]
+    let base = env_path("XDG_DATA_HOME")
+        .filter(|path| path.is_absolute())
+        .or_else(|| env_path("HOME").map(|home| home.join(".local/share")));
+    base.unwrap_or_else(std::env::temp_dir)
+        .join(".openprestige")
+}
+
+pub fn initialize() -> io::Result<PathBuf> {
+    let root = root();
+    for name in ["configs", "logs", "runtime"] {
+        std::fs::create_dir_all(root.join(name))?;
+    }
+    Ok(root)
+}
+
+pub fn native_log(pid: u32) -> PathBuf {
+    root()
+        .join("logs")
+        .join(format!("prestige-native-{pid}.log"))
+}