Fix JS execution: wrap all scripts in IIFEs to avoid WebKit global scope conflicts

WebKit's WKWebView rejects top-level const/let declarations that shadow
global function names. Since utils.js defines functions like stateLabel()
at the global scope (non-module scripts), and later files destructure
the same names from window.NexusTerminal using const, WebKit throws:
  SyntaxError: Can't create duplicate variable that shadows a global property

Fix: wrap every JS file in an IIFE so all declarations are function-scoped.
Also remove temporary diagnostic instrumentation.

frontend/src/js/terminal.js

@@ -1,3 +1,4 @@
+(function() {
 /**
  * Nexus Terminal — xterm.js terminal manager.
  * Creates, manages, and destroys xterm.js instances for SSH and Telnet sessions.
@@ -287,3 +288,5 @@ class TerminalManager {
 
 window.NexusTerminal = window.NexusTerminal || {};
 window.NexusTerminal.TerminalManager = TerminalManager;
+
+})();