feat(dashboard): the daily-overview band becomes opt-in

The hero renders only when the layout carries the literal
heroVisible: true. Legacy blobs without the field, malformed values,
and fresh accounts all keep it off; the Settings toggle persists an
explicit opt-in through the existing layout PUT.

src/app/api/dashboard/widgets/__tests__/route.test.ts

@@ -477,7 +477,7 @@ describe("PUT /api/dashboard/widgets — heroVisible thread-through", () => {
     expect(updateArg.data.dashboardWidgetsJson.heroVisible).toBe(false);
   });
 
-  it("defaults heroVisible to true for a first save with no stored layout", async () => {
+  it("defaults heroVisible to false for a first save with no stored layout", async () => {
     vi.mocked(prisma.user.findUnique).mockResolvedValue({
       dashboardWidgetsJson: null,
     } as never);
@@ -495,7 +495,7 @@ describe("PUT /api/dashboard/widgets — heroVisible thread-through", () => {
       .calls[0]?.[0] as unknown as {
       data: { dashboardWidgetsJson: { heroVisible: boolean } };
     };
-    expect(updateArg.data.dashboardWidgetsJson.heroVisible).toBe(true);
+    expect(updateArg.data.dashboardWidgetsJson.heroVisible).toBe(false);
   });
 
   it("422s on a non-boolean heroVisible", async () => {

src/app/api/dashboard/widgets/route.ts

@@ -283,7 +283,7 @@ export const PUT = apiHandler(async (request: NextRequest) => {
       mergedChartOverlayPrefs = existingLayout.chartOverlayPrefs ?? {};
     }
     if (mergedHeroVisible === undefined) {
-      mergedHeroVisible = existingLayout.heroVisible !== false;
+      mergedHeroVisible = existingLayout.heroVisible === true;
     }
   }
   const normalized = serializeDashboardLayout({