fix: Streaming-Navigation-Bugs (doppelte Messages, client_disconnected), Tool-Result ohne Truncation

- _chatAbandoned-Flag statt AbortController: Backend-Stream läuft bei Navigation weiter, Frontend ignoriert Events
- stopHistoryPolling() während Streaming-Poll aktiv, verhindert parallele Polls
- _pollLock in pollHistory() gegen Race-Conditions bei gleichzeitigen Poll-Aufrufen
- Tool-Result truncate(300) im Live-Chat entfernt, in History beibehalten
- Dashboard Badge-Styling verfeinert

wwwroot/js/ui.js

@@ -238,7 +238,7 @@ function renderToolBoxContent(div, name, inputJson, result, isError) {
 
     const resultDiv = document.createElement('div');
     resultDiv.className = 'tool-result' + (isError ? ' tool-error' : '');
-    resultDiv.textContent = result ? truncate(result, 300) : '';
+    resultDiv.textContent = result || '';
     resultDiv.hidden = true;
     div.appendChild(resultDiv);
     foldTarget = resultDiv;
@@ -340,12 +340,12 @@ function appendToolResult(result, isError) {
 
   const existing = lastBox.querySelector('.tool-result');
   if (existing) {
-    existing.textContent = truncate(result, 300);
+    existing.textContent = result || '';
     if (isError) existing.classList.add('tool-error');
   } else {
     const resultDiv = document.createElement('div');
     resultDiv.className = 'tool-result' + (isError ? ' tool-error' : '');
-    resultDiv.textContent = truncate(result, 300);
+    resultDiv.textContent = result || '';
     resultDiv.hidden = true;
     lastBox.appendChild(resultDiv);
   }