Update newsletter/brand copy, hide VAT section without a vatId, relabel Lebensuhr breadcrumb

- Newsletter panel + modal: new title/description copy, weekly cadence wording
- Brand mentions ("einfach-produktiv") switched to "einfach produktiv."
- Impressum: Umsatzsteuer section (heading + TOC entry) only renders when vatId is set
- /lebensuhr breadcrumb eyebrow now reads "Lebensuhr" instead of "7-Tage-Challenge"

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>

app/components/Hero.tsx

@@ -147,7 +147,7 @@ export function Hero() {
               ))}
             </div>
             <p className="flex-[1_0_0] font-normal leading-[1.5rem] text-text-primary text-body text-center sm:text-left [word-break:break-word]">
-              1.120+ Menschen vertrauen <span className="whitespace-nowrap">einfach-produktiv</span>
+              1.120+ Menschen vertrauen <span className="whitespace-nowrap">einfach produktiv.</span>
             </p>
           </div>
         </Reveal>