Rename /lebensuhr to /7-tage-klarheits-check, update CTA/content copy

Renames the route, its canonical/OG metadata, Navbar's active-route
list, and the testimonials page filter to match. Also updates CTA
copy ("Klarheits-Check starten"), the "So funktioniert" heading, the
"3. Umsetzen" step text, and the breadcrumb label.

app/lib/payload.ts

@@ -817,7 +817,7 @@ export async function getWerkzeugeCards(): Promise<WerkzeugeCard[]> {
   }));
 }
 
-export type TestimonialsPage = "todo-cards" | "newsletter" | "challenge" | "der-eine";
+export type TestimonialsPage = "todo-cards" | "newsletter" | "klarheits-check" | "der-eine";
 
 export type Testimonial = { id: number; quote: string; name: string; role: string; avatar: string };
 
@@ -842,7 +842,7 @@ export function mapPayloadTestimonial(doc: PayloadTestimonial): Testimonial {
 }
 
 // Powers the identically-styled customer testimonial grids on /todo-cards,
-// /newsletter, /challenge, and /der-eine (see TestimonialsGrid.tsx) —
+// /newsletter, /7-tage-klarheits-check, and /der-eine (see TestimonialsGrid.tsx) —
 // previously hardcoded arrays kept manually in sync. The single-quote
 // "photo band" testimonials on /not-found and /bestellbestaetigung are a
 // different shape (no avatar/role) and are not part of this collection.