feat(app): app page at /, mockup gallery moved to /mockups/

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

src/app/index.html

@@ -0,0 +1,19 @@
+<!doctype html>
+<html lang="en">
+<head>
+  <meta charset="utf-8" />
+  <meta name="viewport" content="width=device-width, initial-scale=1" />
+  <title>EPIC: The Musical Timeline — an unofficial fan voyage</title>
+  <link rel="stylesheet" href="../shared/credits.css" />
+  <link rel="stylesheet" href="./style.css" />
+</head>
+<body>
+  <main id="voyage-app">
+    <section id="stage" aria-label="The voyage"></section>
+    <aside id="panel" aria-label="Song details"></aside>
+    <nav id="timeline" aria-label="Songs and motif threads"></nav>
+  </main>
+  <footer data-fan-credits></footer>
+  <script type="module" src="./main.ts"></script>
+</body>
+</html>