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/About.tsx

@@ -29,7 +29,7 @@ export function About() {
         {/* Quote row: script quote / divider / author bio — side-by-side
             only from lg: (1024px), a deliberate exception to the site's
             sm: (640px) structural consolidation: quote + divider + the
-            whitespace-nowrap bio ("Gründer von einfach-produktiv.")
+            whitespace-nowrap bio ("Gründer von einfach produktiv.")
             together need more room than the sm:-anchored text column has
             through the whole 640-1023px range, independent of the outer
             text/image ratio above. Stacked with a horizontal divider
@@ -77,7 +77,7 @@ export function About() {
             <p>Björn.</p>
             <p>Führungskraft.</p>
             <p>Familienmensch.</p>
-            <p>Gründer von einfach-produktiv.</p>
+            <p>Gründer von einfach produktiv.</p>
           </div>
 
         </div>