Let players peek both decks during and after a battle

Record each seat's arranged lineup on the battle result (already public)
and reveal the full deck in a popover when hovering a deck pile in the
battle view — the opponent's included.

web/src/styles.css

@@ -1377,3 +1377,44 @@ h3 {
     transform: scale(1.5);
   }
 }
+
+/* --- deck peek (battle) --- */
+
+.stackpile.peekable {
+  cursor: help;
+}
+
+.deck-peek {
+  position: absolute;
+  bottom: calc(100% + 8px);
+  z-index: 60;
+  width: max-content;
+  max-width: 60vw;
+  background: rgba(18, 53, 31, 0.98);
+  border: 2px solid var(--cocoa);
+  border-radius: 10px;
+  padding: 8px 10px;
+  box-shadow: 0 8px 20px rgba(0, 0, 0, 0.5);
+}
+
+.deck-peek-left {
+  left: 0;
+}
+
+.deck-peek-right {
+  right: 0;
+}
+
+.deck-peek-label {
+  color: var(--gold);
+  font-size: 0.72rem;
+  font-weight: 800;
+  margin-bottom: 6px;
+}
+
+.deck-peek-cards {
+  display: flex;
+  flex-wrap: wrap;
+  gap: 6px;
+  max-width: min(60vw, 560px);
+}