Add DEBUG-gated panel to buy any card in the shop

When the server's DEBUG env var is on, expose a card catalog endpoint
and a collapsible client panel that drops any pet or food straight into
your deck (free, off-turn). Gated server-side so it is inert in normal
play.

web/src/styles.css

@@ -1276,3 +1276,66 @@ h3 {
     height: 110px;
   }
 }
+
+/* --- debug panel (server DEBUG mode) --- */
+
+.debug-panel {
+  position: fixed;
+  top: 64px;
+  right: 0;
+  z-index: 120;
+  display: flex;
+  align-items: flex-start;
+}
+
+.debug-toggle {
+  background: #7a1f1f;
+  color: var(--cream);
+  border: 2px solid var(--cocoa);
+  border-right: none;
+  border-radius: 8px 0 0 8px;
+  font-weight: 800;
+  font-size: 0.8rem;
+  padding: 8px 10px;
+  cursor: pointer;
+  white-space: nowrap;
+  writing-mode: vertical-rl;
+  transform: rotate(180deg);
+}
+
+.debug-panel.is-open .debug-toggle {
+  writing-mode: horizontal-tb;
+  transform: none;
+  border-radius: 8px 0 0 0;
+}
+
+.debug-body {
+  width: min(340px, 80vw);
+  max-height: calc(100vh - 80px);
+  overflow-y: auto;
+  background: rgba(18, 53, 31, 0.97);
+  border: 2px solid var(--cocoa);
+  border-radius: 8px 0 0 8px;
+  padding: 12px;
+  box-shadow: -6px 6px 18px rgba(0, 0, 0, 0.45);
+}
+
+.debug-head {
+  color: var(--gold);
+  font-weight: 800;
+  margin-bottom: 8px;
+}
+
+.debug-tier-label {
+  color: var(--cream);
+  font-size: 0.75rem;
+  font-weight: 700;
+  opacity: 0.8;
+  margin: 8px 0 4px;
+}
+
+.debug-grid {
+  display: flex;
+  flex-wrap: wrap;
+  gap: 6px;
+}