Redesign: warmer, more editorial visual pass; remove stray em dashes

Replaces em dashes with en dashes across all hardcoded copy, emails, and
seed content, then reworks the site's visual language so it reads as
deliberately designed rather than assembled from generic components:

- New ArrowLink component replaces ad hoc "Mehr erfahren ->" links and
  ghost buttons; one shared FormField (TextField/TextAreaField) replaces
  7 near-duplicate field styles across every form
- Navbar loses its glassmorphism blur for a solid warm background, gets a
  subtle active-link underline and a softer, warmer mega-menu
- PageHeader supports per-page blob tone/position and a compact mode
  instead of an identical band on every interior page
- Homepage: the core offer is featured large instead of four equal cards,
  the philosophy section gets a single calmer accent blob, blog teasers
  now show their cover image like the real /aktuelles page does
- Booking calendar and widget: 44px touch targets throughout (month nav,
  day cells, time slots, cancel action), a visible "today" ring, and
  responsive padding so the calendar isn't cramped on small screens
- Quieter, warmer empty states on /termine and /aktuelles

No functional changes: all interaction logic (nav menus, forms, booking,
CMS data fetching) is untouched, only markup and styling.

components/AngebotCard.tsx

@@ -1,5 +1,6 @@
 import Link from "next/link";
 import { ImagePlaceholder } from "@/components/ImagePlaceholder";
+import { ArrowIcon } from "@/components/ArrowIcon";
 import type { ImageMood } from "@/lib/angebote";
 
 type AngebotCardProps = {
@@ -42,9 +43,7 @@ export function AngebotCard({
           <p className="mt-2 text-sm leading-relaxed text-white/90">{tagline}</p>
           <span className="mt-4 inline-flex items-center gap-1.5 text-sm font-medium text-white/95">
             Mehr erfahren
-            <svg width="14" height="10" viewBox="0 0 14 10" fill="none" aria-hidden="true" className="transition-transform duration-300 group-hover:translate-x-1">
-              <path d="M1 5h11.5M8 1l4.5 4L8 9" stroke="currentColor" strokeWidth="1.4" strokeLinecap="round" strokeLinejoin="round" />
-            </svg>
+            <ArrowIcon />
           </span>
         </div>
       </div>