Remove the 5-model limit on multi-run groups

The per-group cap of 5 models was enforced in three client-side locations with no server-side constraint and no technical justification; the store iterates models in a plain loop and dispatches each run via Promise.allSettled. Remove the cap entirely from MultiRunLauncher, useMultiRunStore, and AgentManagerEmptyState, and drop the {max} ceiling from the launcher info copy across all locales.

Closes #2847

packages/ui/src/components/multirun/MultiRunLauncher.tsx

@@ -32,7 +32,6 @@ import { startDesktopWindowDrag } from '@/lib/desktopNative';
 import { useI18n } from '@/lib/i18n';
 
 const MAX_FILE_SIZE = 10 * 1024 * 1024;
-const MAX_MODELS_PER_GROUP = 5;
 
 interface MultiRunAttachedFile {
   id: string;
@@ -727,7 +726,6 @@ const RunGroupCard: React.FC<RunGroupCardProps> = ({
   const snippetRef = React.useRef<SnippetAutocompleteHandle>(null);
 
   const handleAddModel = React.useCallback((model: ModelSelectionWithId) => {
-    if (group.models.length >= MAX_MODELS_PER_GROUP) return;
     onUpdate(group.id, { models: [...group.models, model] });
   }, [group.id, group.models, onUpdate]);
 
@@ -987,7 +985,7 @@ const RunGroupCard: React.FC<RunGroupCardProps> = ({
       <div className="flex flex-col gap-1.5">
         <FieldLabel
           required
-          info={<InfoTip>{t('multirun.launcher.models.info', { max: MAX_MODELS_PER_GROUP })}</InfoTip>}
+          info={<InfoTip>{t('multirun.launcher.models.info')}</InfoTip>}
         >
           {t('multirun.launcher.models.label')}
         </FieldLabel>
@@ -997,7 +995,6 @@ const RunGroupCard: React.FC<RunGroupCardProps> = ({
           onRemove={handleRemoveModel}
           onUpdate={handleUpdateModel}
           minModels={1}
-          maxModels={MAX_MODELS_PER_GROUP}
         />
       </div>
     </div>