feat: API Key pro Agent statt pro User

- Neue Tabelle agent_api_keys (user_id, agent_id, key_id)
- Migration: bestehende selected_api_key_id auf alle Agents verteilt
- Backend: GetAgentApiKeyRecord(userId, agentId) in Chat, Telegram, Cronjobs
- Endpoints: select/selected mit ?agentId Query-Parameter
- Frontend: currentAgentId aus Session, alle Key-Calls agent-aware
- DeleteApiKey bereinigt agent_api_keys statt users.selected_api_key_id

wwwroot/js/pages/chat-page.js

@@ -49,7 +49,7 @@ async function _initChatUsageBadge() {
   if (!container) return;
 
   try {
-    var selectedKey = await apiGetSelectedKey();
+    var selectedKey = await apiGetSelectedKey(getCurrentAgentId());
     if (!selectedKey || !selectedKey.selected) {
       container.innerHTML = '';
       var noKeyBtn = document.createElement('button');
@@ -85,7 +85,7 @@ async function _refreshChatUsageBadge() {
   var container = document.getElementById('chatUsageBadge');
   if (!container || !_chatUsageKeyId) return;
   try {
-    var selectedKey = await apiGetSelectedKey();
+    var selectedKey = await apiGetSelectedKey(getCurrentAgentId());
     if (selectedKey) _renderChatUsageBadge(container, selectedKey);
   } catch(e) { /* ignore */ }
 }
@@ -119,7 +119,7 @@ function _renderChatUsageBadge(container, key) {
       checkBtn.querySelector('i').className = 'fa fa-spinner fa-spin';
       try {
         await apiCheckApiKey(_chatUsageKeyId);
-        var selectedKey = await apiGetSelectedKey();
+        var selectedKey = await apiGetSelectedKey(getCurrentAgentId());
         if (selectedKey) _renderChatUsageBadge(container, selectedKey);
       } catch(e) {
         console.error('Key check failed:', e);
@@ -136,7 +136,7 @@ async function _showKeySwitchModal() {
   try { keys = await apiGetAvailableKeys(); } catch(e) { return; }
 
   var selectedKey = null;
-  try { selectedKey = await apiGetSelectedKey(); } catch(e) { /* ignore */ }
+  try { selectedKey = await apiGetSelectedKey(getCurrentAgentId()); } catch(e) { /* ignore */ }
   var selectedKeyId = selectedKey ? selectedKey.keyId : null;
 
   var { body, close } = _createModal('API Key wechseln', { modal: 'key-switch-modal' });
@@ -187,7 +187,7 @@ async function _showKeySwitchModal() {
       row.addEventListener('click', async function() {
         row.classList.add('loading-state');
         try {
-          await apiSelectApiKey(key.keyId);
+          await apiSelectApiKey(key.keyId, getCurrentAgentId());
           close();
           await _initChatUsageBadge();
         } catch(e) {
@@ -352,6 +352,8 @@ registerPage('chat', {
       return;
     }
 
+    currentAgentId = session.agentId;
+
     const titleEl = document.getElementById('sessionTitle');
     if (titleEl) {
       titleEl.textContent = session.name || 'Unbenannt';
@@ -605,6 +607,7 @@ registerPage('chat', {
     _chatAbandoned = true;
     stopTypingIndicator();
     setCurrentAgentName(null);
+    currentAgentId = null;
     closeEmojiPicker();
     // Usage Badge cleanup
     if (_chatUsageScrollHandler) {