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/agent-page.js

@@ -36,6 +36,7 @@ registerPage('agent', {
     const addCommandBtn = document.getElementById('agentAddCommandBtn');
     const skillsSection = document.getElementById('agentSkillsSection');
     const skillList = document.getElementById('agentSkillList');
+    const more = document.querySelector('.more');
 
     _agentAvatarData = null;
 
@@ -120,6 +121,13 @@ registerPage('agent', {
       }
     });
 
+    more.addEventListener('click', () => {
+      const content = more.querySelector('[hidden]');
+      while (content.firstChild)
+          more.parentNode.insertBefore(content.firstChild, more);
+      more.remove();
+    });
+
     // Speichern
     saveBtn.addEventListener('click', async () => {
       const data = {