User invite uses external domain option (#118)

* feat: user invite uses external domain option
fixes #117

* fix: inconsistent external url format

* fix: normalize external url more cleanly

server/internal/config/sys-conf.ts

@@ -1,8 +1,13 @@
+import normalizeUrl from "normalize-url";
+
 class SystemConfig {
   private libraryFolder = process.env.LIBRARY ?? "./.data/library";
   private dataFolder = process.env.DATA ?? "./.data/data";
 
-  private externalUrl = process.env.EXTERNAL_URL ?? "http://localhost:3000";
+  private externalUrl = normalizeUrl(
+    process.env.EXTERNAL_URL ?? "http://localhost:3000",
+    { stripWWW: false },
+  );
   private dropVersion;
   private gitRef;