fix(insights): point the ECG cross-link at the routed sub-page

Repoint EcgCrossLink from the overview `#ecg` fragment to `/insights/ecg`.
The fragment is absent until the overview section's own fetch resolves, so
the deep link no-oped on navigation (UX-flows finding F1-1); the routed
sub-page always mounts.

src/app/insights/__tests__/ecg-cross-link-mount.test.tsx

@@ -89,12 +89,12 @@ describe("EcgCrossLink mount on Heart sub-pages (H1)", () => {
   it("mounts the ECG cross-link on the resting-pulse page", () => {
     const html = render(<RestingPulsePage />);
     expect(html).toContain('data-slot="ecg-cross-link"');
-    expect(html).toContain('href="/insights#ecg"');
+    expect(html).toContain('href="/insights/ecg"');
   });
 
   it("mounts the ECG cross-link on the HRV page", () => {
     const html = render(<HrvPage />);
     expect(html).toContain('data-slot="ecg-cross-link"');
-    expect(html).toContain('href="/insights#ecg"');
+    expect(html).toContain('href="/insights/ecg"');
   });
 });

src/components/insights/__tests__/ecg-cross-link.test.tsx

@@ -62,7 +62,7 @@ describe("<EcgCrossLink>", () => {
       hasRecordings: true,
     });
     expect(html).toContain('data-slot="ecg-cross-link"');
-    expect(html).toContain('href="/insights#ecg"');
+    expect(html).toContain('href="/insights/ecg"');
     expect(html).toContain("2 recordings on file.");
     // The latest (first) recording's DEVICE result, attributed to the device.
     expect(html).toContain("Latest device result:");

src/components/insights/ecg-cross-link.tsx

@@ -13,7 +13,9 @@ import { TileHeader } from "@/components/insights/tile-header";
 
 /**
  * S10 — ECG cross-link, the pointer from the resting-HR / pulse context into
- * the ECG viewer (`/insights#ecg`).
+ * the ECG viewer (`/insights/ecg`). Points at the routed sub-page, which
+ * always mounts, rather than the overview `#ecg` fragment, which is absent
+ * until the overview section's own fetch resolves (UX-flows finding F1-1).
  *
  * NON-DIAGNOSTIC (load-bearing, mirrors `EcgSection` / `RhythmEventsCard`): the
  * card surfaces ONLY that recordings exist + the RECORDING DEVICE's OWN latest
@@ -86,7 +88,7 @@ export function EcgCrossLink({ enabled = true, className }: EcgCrossLinkProps) {
 
   return (
     <Link
-      href="/insights#ecg"
+      href="/insights/ecg"
       data-slot="ecg-cross-link"
       className={cn(
         // `.metric-accent` — the heart-family identity edge (`--tile-strain`,