fix: Distributed API proxy memory leak, node switcher refresh, and copy button

Proxy memory leak (MaxListenersExceededWarning + DEP0060):
createProxyMiddleware was instantiated inside the request handler on every
single API call. Each new instance registered fresh 'close' listeners on the
HTTP server and re-ran the http-proxy util._extend deprecated path. After ~10
requests the MaxListeners threshold was breached. Fix: declare ONE global
remoteNodeProxy at startup using the router option to dynamically resolve the
target URL per request. Listeners are registered once. ECONNREFUSED errors are
caught in the on.error handler and returned as structured 502 JSON.

Node switcher "nothing happens":
EditorLayout had a single useEffect([], []) that called refreshStacks() once
on mount. Changing the active node updated NodeContext state and localStorage
but nothing re-triggered the stack list fetch. Fix: split into two effects —
notifications polling (no dependency) and a stack-refresh effect keyed on
activeNode?.id. When the node changes, stale editor/container/file state is
cleared and the stacks for the new node are fetched.

Copy button silently failing:
navigator.clipboard.writeText() throws DOMException in non-HTTPS / non-localhost
contexts (e.g. http://192.168.x.x). The uncaught async exception silently
swallowed the success toast and state update. Fix: wrapped in try/catch with
an execCommand('copy') textarea fallback and a final error toast if both fail.

frontend/src/components/EditorLayout.tsx

@@ -147,12 +147,27 @@ export default function EditorLayout() {
     }
   };
 
+  // Notification polling — independent of active node, runs once on mount
   useEffect(() => {
-    refreshStacks();
     fetchNotifications();
     const notificationInterval = setInterval(fetchNotifications, 5000);
     return () => clearInterval(notificationInterval);
-  }, []);
+  }, []); // eslint-disable-line react-hooks/exhaustive-deps
+
+  // Re-fetch stacks whenever the active node changes (or becomes available on mount).
+  // Also clears any stale editor/container state that belonged to the previous node.
+  useEffect(() => {
+    if (!activeNode) return;
+    setSelectedFile(null);
+    setContent('');
+    setOriginalContent('');
+    setEnvContent('');
+    setOriginalEnvContent('');
+    setContainers([]);
+    setIsEditing(false);
+    setActiveView('dashboard');
+    refreshStacks();
+  }, [activeNode?.id]); // eslint-disable-line react-hooks/exhaustive-deps
 
   const fetchNotifications = async () => {
     try {

frontend/src/components/NodeManager.tsx

@@ -177,10 +177,31 @@ export function NodeManager() {
 
   const copyToken = async () => {
     if (!generatedToken) return;
-    await navigator.clipboard.writeText(generatedToken);
-    setTokenCopied(true);
-    toast.success('Token copied to clipboard');
-    setTimeout(() => setTokenCopied(false), 2000);
+    try {
+      // Clipboard API requires a secure context (HTTPS or localhost)
+      await navigator.clipboard.writeText(generatedToken);
+      setTokenCopied(true);
+      toast.success('Token copied to clipboard');
+      setTimeout(() => setTokenCopied(false), 2000);
+    } catch {
+      // Fallback for HTTP / non-localhost deployments where Clipboard API is unavailable
+      try {
+        const ta = document.createElement('textarea');
+        ta.value = generatedToken;
+        ta.style.position = 'fixed';
+        ta.style.opacity = '0';
+        document.body.appendChild(ta);
+        ta.focus();
+        ta.select();
+        document.execCommand('copy');
+        document.body.removeChild(ta);
+        setTokenCopied(true);
+        toast.success('Token copied to clipboard');
+        setTimeout(() => setTokenCopied(false), 2000);
+      } catch {
+        toast.error('Could not copy automatically — please select and copy the token manually.');
+      }
+    }
   };
 
   const getStatusBadge = (status: string) => {