Collapse between-scenes upkeep into a single panel

During between_scenes there's now just one centered panel with the
voting controls, nomination progress, and Crew Rank Ledger. The separate
"Resting Deep Upkeep" panel (which only said hand refresh would happen
later) is rendered solely during deep_upkeep, where the actual discard/
redraw happens. Moved the rank ledger into the voting panel and added a
.between-grid.single layout.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

frontend/src/assets/css/upkeep.css

@@ -6,6 +6,14 @@
     margin: 2rem 0;
 }
 
+/* Between scenes there's only the voting/roster panel — center it. */
+.between-grid.single {
+    grid-template-columns: 1fr;
+    max-width: 640px;
+    margin-left: auto;
+    margin-right: auto;
+}
+
 @media (max-width: 800px) {
     .between-grid {
         grid-template-columns: 1fr;