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/stores/useMultiRunStore.test.ts

@@ -226,4 +226,20 @@ describe('useMultiRunStore', () => {
       'createSession:/repo-worktrees/fix-thing',
     ]);
   });
+
+  test('accepts more than 5 models per group without a "maximum 5 models" error', async () => {
+    const models = Array.from({ length: 6 }, (_, i) => ({
+      providerID: 'anthropic',
+      modelID: `claude-sonnet-4-5-${i}`,
+    }));
+
+    const result = await useMultiRunStore.getState().createMultiRun({
+      name: 'Many models',
+      isolateRuns: false,
+      groups: [{ prompt: 'Fix it', models }],
+    });
+
+    expect(useMultiRunStore.getState().error).toBeNull();
+    expect(result?.sessionIds).toHaveLength(6);
+  });
 });

packages/ui/src/stores/useMultiRunStore.ts

@@ -138,10 +138,6 @@ export const useMultiRunStore = create<MultiRunStore>()(
             set({ error: `Group ${gi + 1}: select at least 1 model` });
             return null;
           }
-          if (groups[gi].models.length > 5) {
-            set({ error: `Group ${gi + 1}: maximum 5 models allowed` });
-            return null;
-          }
         }
 
         set({ isLoading: true, error: null });