Keep the downloaded catalog in the user's own Ghidra settings directory.

The extension is installed system wide and is therefore read-only, so
refreshing the catalog into its own data/ directory fails for every user that
is not root. Only the copy that ships with the extension is read from there,
and only until a newer one has been downloaded.

--- a/src/main/java/extensionmanager/catalog/CatalogUtils.java	2026-08-28 05:26:50.000000000 -0400
+++ b/src/main/java/extensionmanager/catalog/CatalogUtils.java	2026-09-11 11:03:36.211968684 -0400
@@ -26,7 +26,11 @@
 
 	private static Catalog catalog;
 
-	private static File getCatalogFile() {
+	/**
+	 * The copy of the catalog that ships with the extension. It is read-only
+	 * when the extension is installed system wide.
+	 */
+	private static File getPackagedCatalogFile() {
 		try {
 			ResourceFile resourceFile = Application.getModuleDataFile("catalog.json");
 			return resourceFile.getFile(true);
@@ -38,10 +42,25 @@
 		return null;
 	}
 
+	/**
+	 * The downloaded catalog, kept in the user's own settings directory so that
+	 * updating it never needs write access to the extension itself.
+	 */
+	private static File getUserCatalogFile() {
+		return new File(Application.getUserSettingsDirectory(), "extensionmanager-catalog.json");
+	}
+
+	private static File getCatalogFile() {
+		File userFile = getUserCatalogFile();
+		if (userFile.isFile())
+			return userFile;
+		return getPackagedCatalogFile();
+	}
+
 	public static boolean update() {
 		log.trace("Updating catalog...");
 		try {
-			File file = getCatalogFile();
+			File file = getUserCatalogFile();
 			URL url = new URI(
 					"https://github.com/antoniovazquezblanco/GhidraExtensionManagerRepository/releases/download/latest/catalog.json")
 					.toURL();