feat: the homepage leads the visitor through as one story

The page was a row of sections to scroll past, and a film in one of them did
not change that. It now follows the questions a visitor has, in the order
they come up: who is this, can he do what I need, what does it look like,
what else, how does it go, has he done it, what is open, how do I start.

Each chapter ends by asking the next question as a large link that leads on,
and the next chapter answers it. A rail at the edge shows every chapter as a
station with a dot travelling along it (on phones: a pill with the current
chapter and one tap to the next), and the header names the current question.

Where the visitor is, is pure logic in src/domain/chapters.ts. The scroll
film section and the bridge sentences are removed.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

apps/web/src/components/Header.tsx

@@ -9,6 +9,7 @@ import { DecodeText } from "./bits/DecodeText";
 import { ScrollBits } from "./bits/ScrollBits";
 import { useContent, useLocale } from "./ContentProvider";
 import { LanguageSwitch } from "./LanguageSwitch";
+import { ChapterNow } from "./story/StoryGuide";
 
 /** Header: the logo, the link to the freelance page, the language switch and one action. */
 export const Header: React.FC = () => {
@@ -61,7 +62,11 @@ export const Header: React.FC = () => {
           </div>
         </Link>
 
-        <ScrollBits className="hidden font-mono text-[10px] tracking-[0.3em] text-slate-400 md:block" />
+        <ChapterNow
+          fallback={
+            <ScrollBits className="hidden font-mono text-[10px] tracking-[0.3em] text-slate-400 md:block" />
+          }
+        />
 
         <div className="flex items-center gap-2.5 md:gap-4">
           <Link