Add multi-model panel with Fusion mode

Panel agents answer the user prompt in parallel (read-only, non-streaming);
their responses are merged into the worker's last user message as a
<panel_responses> block, and the session agent synthesizes one final
streamed answer. The RunPanel engine is built layer-ready for future MoA.

- New session fields: multi_model_mode (off/fusion), panel_agent_ids (CSV)
  with idempotent column migration
- New partial Services/AnthropicService.Panel.cs holding the RunPanel engine
- Provider-agnostic members: Anthropic RunNonStreamingToolLoop / OpenAI
  CompleteText / CLI plan-mode; all forced read-only, persisted with Tag=panel
- SSE events: panel_start, panel_member_start, panel_member_done, panel_done
- Frontend: multi-agent picker, live panel bubbles, history rendering
- Graceful degradation: panel errors fall back to worker-only

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

wwwroot/js/pages/session-page.js

@@ -29,6 +29,10 @@ registerPage('session', {
     const maxReviewIterationsEl = document.getElementById('maxReviewIterations');
     const finalizerAgentSelect = document.getElementById('finalizerAgentSelect');
     const finalizerAgentSelectCard = document.getElementById('finalizerAgentSelectCard');
+    const panelModeEl = document.getElementById('multiModelMode');
+    const panelAgentsRow = document.getElementById('panelAgentsRow');
+    const panelAgentsCard = document.getElementById('panelAgentsCard');
+    const panelAgentIdsEl = document.getElementById('panelAgentIds');
     const imagePreview = document.getElementById('sessionImagePreview');
     const saveBtn = document.getElementById('sessionSaveBtn');
     const cancelBtn = document.getElementById('sessionCancelBtn');
@@ -126,6 +130,38 @@ registerPage('session', {
     updateReviewVisibility();
     setupAgentPicker(finalizerAgentSelectCard, finalizerAgentSelect, session && session.finalizerAgentId, 'fa-flag-checkered', 'Kein Finalizer-Agent');
 
+    // Multi-Modell-Panel (Fusion): Modus + Mehrfach-Agenten-Picker
+    function renderPanelInCard() {
+      var ids = (panelAgentIdsEl.value || '').split(',').map(function(s){ return s.trim(); }).filter(Boolean);
+      if (ids.length === 0) {
+        panelAgentsCard.innerHTML = '<div class="agent-select-empty"><i class="fa fa-users"></i> Keine Panel-Agenten</div>';
+        return;
+      }
+      var chips = ids.map(function(id) {
+        var a = agentMap[id];
+        var label = a ? a.name : id.slice(0, 8);
+        var model = a ? ((typeof prettyModelName === 'function') ? prettyModelName(a.model) : a.model) : '';
+        return '<span class="badge">' + esc(label) + (model ? ' · ' + esc(model) : '') + '</span>';
+      }).join(' ');
+      panelAgentsCard.innerHTML = '<div style="display:flex;flex-wrap:wrap;gap:4px;align-items:center">' + chips + '</div>'
+        + '<span class="agent-select-change"><i class="fa fa-pencil"></i></span>';
+    }
+    function updatePanelVisibility() {
+      panelAgentsRow.hidden = (panelModeEl.value === 'off');
+    }
+    panelModeEl.value = (session && session.multiModelMode) || 'off';
+    panelAgentIdsEl.value = (session && session.panelAgentIds) || '';
+    renderPanelInCard();
+    updatePanelVisibility();
+    panelModeEl.addEventListener('change', updatePanelVisibility);
+    panelAgentsCard.addEventListener('click', function() {
+      var currentIds = (panelAgentIdsEl.value || '').split(',').map(function(s){ return s.trim(); }).filter(Boolean);
+      openMultiAgentPickerModal(agents, agentSkillsMap, currentIds, function(newIds) {
+        panelAgentIdsEl.value = newIds.join(',');
+        renderPanelInCard();
+      });
+    });
+
     // User-Zuweisung (jeder Besitzer, nur für bestehende Sessions)
     if (!isNew) {
       initSessionUserPicker(ownerRow, userSelectCard, userSelect, session && session.userId);
@@ -177,6 +213,8 @@ registerPage('session', {
         maxReviewIterations: parseInt(maxReviewIterationsEl.value) || 3,
         finalizerAgentId: finalizerAgentSelect.value || null,
         preparerAgentId: preparerAgentSelect.value || null,
+        multiModelMode: panelModeEl.value || 'off',
+        panelAgentIds: panelAgentIdsEl.value || null,
         context: _sessionContextMde.value().trim() || null,
         workspace: workspaceEl.value.trim() || null,
         customCommands: commands,
@@ -247,6 +285,16 @@ function openAgentPickerModal(agents, agentSkillsMap, currentId, onSelect) {
   });
 }
 
+function openMultiAgentPickerModal(agents, agentSkillsMap, selectedIds, onConfirm) {
+  const items = agents.map(a => {
+    a._pickerId = a.agentId;
+    return a;
+  });
+  _openMultiPickerModal('Panel-Agenten auswählen', items, selectedIds, onConfirm, {
+    buildCard: (a) => buildAgentCard(a, agentSkillsMap[a.agentId] || [])
+  });
+}
+
 function initSessionTelegram(sessionId, session) {
   var botSelectCard = document.getElementById('telegramBotSelectCard');
   var botSelect = document.getElementById('telegramBotSelect');