Generalize MCP servers, add model refresh button, add sonnet-5

- MCP: replace fixed single Unity field with a generic list of servers
  ({name, url, token?}); dynamic mcp-config + allowlist glob mcp__*<name>*
  per entry; new mcp-servers-ui.js editor (no data migration)
- Models: frontend refresh button wired to existing POST /api/models/refresh,
  reloads optgroups and restores selection
- Model: add sonnet-5 alias + dropdown option (bare "sonnet" stays 4.6)

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

wwwroot/js/api.js

@@ -252,6 +252,9 @@ function apiDeleteApiKey(id) { return _del('/api/admin/api-keys/' + id, 'Fehler
 function apiCheckApiKey(id) { return _post('/api/admin/api-keys/' + id + '/check', undefined, 'Fehler beim Prüfen'); }
 function apiCheckAllApiKeys() { return _post('/api/admin/api-keys/check-all', undefined, 'Fehler beim Prüfen'); }
 
+// ── Models API ──
+function apiRefreshModels() { return _post('/api/models/refresh', undefined, 'Fehler beim Neu-Laden der Modelle'); }
+
 // ── Key Scanner API (Admin) ──
 
 function apiTriggerScan(mode) { return _post('/api/admin/api-keys/scan?mode=' + (mode || 'full'), undefined, 'Fehler beim Starten des Scans'); }