Fix #169: persistent full-width divider under stats dropdown title

The divider between the stats dropdown head and body lived on
.stats-body's border-top, so it vanished when collapsed and only the
hover background hinted at the boundary (flicker). Move it to
.stats-head border-bottom so it is always present and spans the full
pill width.

internal/web/static/app.css

@@ -217,13 +217,13 @@ body {
 .paste-title-bar { display: flex; align-items: center; gap: 12px; padding: 12px 18px; flex-wrap: wrap; }
 .paste-title-bar h1 { font-size: 29.2px; font-weight: 600; margin: 0; word-break: normal; overflow-wrap: anywhere; }
 .stats-pill { border: 1px solid var(--border); border-radius: var(--radius); overflow: hidden; }
-.stats-head { display: flex; align-items: center; gap: 16px; width: 100%; background: none; border: 0; color: var(--muted-fg); font: inherit; font-size: 21.6px; padding: 14px 18px; cursor: pointer; text-align: left; }
+.stats-head { display: flex; align-items: center; gap: 16px; width: 100%; background: none; border: 0; border-bottom: 1px solid var(--border); color: var(--muted-fg); font: inherit; font-size: 21.6px; padding: 14px 18px; cursor: pointer; text-align: left; }
 .stats-head:hover { color: var(--fg); background: var(--surface-2); }
 .stats-chev { width: 18px; height: 18px; flex: none; transition: transform 0.15s ease; }
 .stats-pill.open .stats-chev { transform: rotate(180deg); }
 .stats-summary { overflow: hidden; text-overflow: ellipsis; white-space: nowrap; letter-spacing: .01em; }
 @media (max-width: 640px) { .stats-summary { white-space: normal; word-break: break-word; } }
-.stats-body { border-top: 1px solid var(--border); }
+.stats-body { /* #169: divider under the dropdown title is the head's own persistent border-bottom */ }
 .stats-grid { display: grid; grid-template-columns: max-content 1fr; gap: 6px 18px; padding: 12px 16px; font-size: 20.7px; }
 .stats-k { color: var(--muted-fg); }
 .stats-v { color: var(--fg); word-break: break-all; }