fix(story): smooth hero overlay fade-out and add scrolly caption background

Overlay previously hard-hid with display:none when scrollY = 100vh, while
the title was still visible (it exits at ~115vh). Now fades in 0→0.65 over
the first 70vh then fades back out to 0 by 140vh (full hero height).

Scrolly caption changed from full-width to centered pill with
rgba(0,0,0,0.45) background — readable against any image regardless of tone.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01Vgmzx8VTTTmCskSpQtsLTr

themes/intotheeast/css/style.css

@@ -1305,14 +1305,23 @@ body::after {
 .scrolly__caption {
     position: absolute;
     bottom: var(--space-4);
-    left: var(--space-4);
-    right: var(--space-4);
+    left: 50%;
+    right: auto;
+    transform: translateX(-50%);
     font-family: var(--font-ui);
     font-size: var(--text-xs);
-    color: rgba(255,255,255,0.65);
+    color: rgba(255,255,255,0.85);
     text-align: center;
     pointer-events: none;
     margin: 0;
+    white-space: nowrap;
+    max-width: 85%;
+    overflow: hidden;
+    text-overflow: ellipsis;
+    background: rgba(0,0,0,0.45);
+    padding: 0.2rem 0.65rem;
+    border-radius: 2px;
+    z-index: 2;
 }
 .scrolly__steps-content { display: none; }
 .scrolly-step { min-height: 60vh; display: flex; align-items: center; padding: var(--space-16) var(--space-8); }