refactor: simplify cleanup() and document why module reload is required

Remove defensive checks that are guaranteed by jsdom-global (window and
document are always set), the jQuery alias for PrivateBin (unused after
jQuery removal), and the conditional re-export block.

The module reload (delete require.cache + re-require) is intentional and
necessary: modules like CopyToClipboard hold DOM element references in
closure variables and schedule setTimeout callbacks. Without a reload,
those callbacks fire against elements from a now-dead jsdom window after
cleanup(), causing cross-test interference. Document this clearly.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

js/common.js

@@ -7,41 +7,19 @@ global.jsdom = require('jsdom-global');
 // initial DOM environment created by jsdom-global
 let currentCleanup = global.jsdom();
 
-// wrap cleanup so that calling it recreates a fresh jsdom environment
+// Recreates the jsdom environment and reloads privatebin.js into it.
+// The reload is necessary because modules close over DOM element references
+// in their init() methods, and pending async callbacks (e.g. setTimeout in
+// CopyToClipboard) would otherwise fire against elements from a dead window.
 global.cleanup = function (...args) {
-    // remove previous environment
     if (typeof currentCleanup === 'function') {
         currentCleanup();
     }
-
-    // create a new jsdom environment
     currentCleanup = global.jsdom(...args);
-
-    // Make sure window and document are available in global scope for module loading
-    // jsdom-global sets them, but we need to ensure they're accessible
-    if (typeof window === 'undefined') {
-        throw new Error('jsdom-global failed to set up window');
-    }
-    if (typeof document === 'undefined') {
-        throw new Error('jsdom-global failed to set up document');
-    }
-
-    // Clear module cache to ensure modules are re-evaluated with new jsdom environment
     delete require.cache[require.resolve('./privatebin')];
     delete require.cache[require.resolve('./legacy')];
     require('./privatebin');
-    if (typeof PrivateBin === 'undefined') {
-        throw new Error('PrivateBin module did not load correctly');
-    }
-
-    // also re-export the PrivateBin namespace if available
-    if (typeof window !== 'undefined' && window.PrivateBin) {
-        global.PrivateBin = window.PrivateBin;
-        if (global.$) {
-            global.$.PrivateBin = window.PrivateBin;
-        }
-    }
-
+    global.PrivateBin = window.PrivateBin;
     return global.cleanup;
 };
 global.fs = require('fs');
@@ -58,15 +36,7 @@ global.DOMPurify = require('./purify-3.4.1');
 global.baseX = require('./base-x-5.0.1').baseX;
 global.Legacy = require('./legacy').Legacy;
 require('./privatebin');
-
-// provide global access to the namespace so tests can reference it directly
-if (typeof window !== 'undefined' && window.PrivateBin) {
-    global.PrivateBin = window.PrivateBin;
-    // keep the old jQuery alias around just in case some tests still use it
-    if (global.$) {
-        global.$.PrivateBin = window.PrivateBin;
-    }
-}
+global.PrivateBin = window.PrivateBin;
 
 // internal variables
 var a2zString    = ['a','b','c','d','e','f','g','h','i','j','k','l','m',