Room planner: fix settings scroll, checkout time to left-bracket sliver

- Settings page: add overflow-y:auto + flex:1 so content scrolls within
  page-content (which has overflow:hidden)

- Checkout time: move departure time out of B2B card stats row and into
  the left-bracket sliver, matching original plugin behaviour:
  - Only shown while prev booking status is still 'arrived' (not yet
    checked out); collapses to normal bracket once NewBook flips to
    'departed'
  - Positioned absolutely over the ::before left bracket area
  - Remove the forced 'departed' override on prev_status — let NewBook's
    real status drive bracket colour so the sliver shows correctly

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

frontend/src/index.css

@@ -444,6 +444,24 @@ html, body, #root {
 .room-card[data-next-status="unconfirmed"]::after { border-color: #f59e0b; }
 .room-card[data-next-status="departed"]::after    { border-color: #a855f7; }
 
+/* Departure time shown in left-bracket sliver (while prev booking still 'arrived') */
+.card-sliver-depart {
+  position: absolute;
+  left: -21px;
+  top: 50%;
+  transform: translateY(-50%);
+  display: flex;
+  flex-direction: column;
+  align-items: center;
+  gap: 1px;
+  font-size: 8px;
+  font-weight: 600;
+  color: var(--col-arrived);
+  line-height: 1;
+  pointer-events: none;
+  white-space: nowrap;
+}
+
 /* Blocked room */
 .room-card.room-blocked {
   background: #4b5563;
@@ -912,6 +930,8 @@ html, body, #root {
 .settings-page {
   padding: 20px;
   max-width: 720px;
+  overflow-y: auto;
+  flex: 1;
 }
 .settings-section {
   background: var(--card-bg);