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/app/globals.css

@@ -1339,6 +1339,23 @@ pre:has(code[class*="language-"]) {
   }
 }
 
+/* The story guide: the dot that travels along the chapter rail, and the header line. */
+.story-dot {
+  box-shadow:
+    0 0 0 3px rgba(253, 230, 138, 0.35),
+    0 0 14px 3px rgba(251, 191, 36, 0.8);
+  transition: top 200ms linear;
+}
+.story-now {
+  animation: story-now-in 400ms cubic-bezier(0.16, 1, 0.3, 1);
+}
+@keyframes story-now-in {
+  from {
+    opacity: 0;
+    transform: translateY(6px);
+  }
+}
+
 /*
  * Native feel: the page should behave like a well-made app on every input type.
  */