feat: shared-page message merging + UI reorganization

Shared Page:
- Merge consecutive assistant text messages (same iteration)
- Add iteration field to thread API response
- Unified rendering for single/thread messages

UI Reorganization (manual changes):
- Session + Agent forms: collapsible 'Weitere Einstellungen' section
- Agent defaults: tool_choice unchecked, web_search 2025, model opus-4-6
- Profile: default-path field hidden, divider removed
- Form spacing adjustments, .more toggle style

wwwroot/js/pages/shared-page.js

@@ -13,23 +13,18 @@ registerPage('shared', {
       const data = await apiGetShared(token);
       container.innerHTML = '';
 
+      let messages = [];
+
       if (data.messages && data.messages.length > 0) {
-        // Mehrere Nachrichten (Thread mit Kontext)
-        data.messages.forEach(msg => {
-          const div = document.createElement('div');
-          div.className = 'msg ' + (msg.role === 'user' ? 'user' : 'assistant') + ' markdown';
-          if (msg.role === 'user') {
-            renderUserContent(div, msg.content);
-          } else {
-            div.innerHTML = renderMarkdown(msg.content);
-            parseFluentEmojis(div);
-            wrapKreaGalleries(div);
-          }
-          container.appendChild(div);
-        });
+        messages = data.messages;
       } else if (data.message) {
-        // Einzelne Nachricht
-        const msg = data.message;
+        messages = [data.message];
+      }
+
+      // Aufeinanderfolgende Assistant-Text-Messages mergen (wie im Chat)
+      messages = _mergeConsecutiveTexts(messages);
+
+      for (const msg of messages) {
         const div = document.createElement('div');
         div.className = 'msg ' + (msg.role === 'user' ? 'user' : 'assistant') + ' markdown';
         if (msg.role === 'user') {
@@ -57,3 +52,20 @@ registerPage('shared', {
   },
   destroy: () => {}
 });
+
+function _mergeConsecutiveTexts(msgs) {
+  const result = [];
+  for (const msg of msgs) {
+    if (msg.role === 'assistant') {
+      const prev = result[result.length - 1];
+      if (prev && prev.role === 'assistant'
+          && prev.iteration === msg.iteration) {
+        prev.content = (prev.content || '') + ' ' + (msg.content || '');
+        if (msg.createdAt) prev.createdAt = msg.createdAt;
+        continue;
+      }
+    }
+    result.push(Object.assign({}, msg));
+  }
+  return result;
+}