fix(inventory): address code review findings

- Replace setTimeout race in use-item flow with explicit Back button
- Fix collector end handler to re-render current view instead of blanking
- Add appendUseBackButton helper to attach navigation to use results
- Remove unused isInventoryInteraction import
- Fix rarity test type assertions

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

bot/modules/inventory/inventory.view.ts

@@ -289,6 +289,34 @@ export function getDiscardConfirmMessage(entry: InventoryEntry, viewerId: string
     };
 }
 
+/**
+ * Wraps a use-item result message with a Back button so the user
+ * can return to the inventory after seeing the effect result.
+ */
+export function appendUseBackButton(message: any, viewerId: string): any {
+    const backRow = new ActionRowBuilder<ButtonBuilder>().addComponents(
+        new ButtonBuilder()
+            .setCustomId(`inv_use_back_${viewerId}`)
+            .setLabel("◀ Back to Inventory")
+            .setStyle(ButtonStyle.Primary)
+    );
+
+    // If CV2 message with components array, append to the first container
+    if (message.components && message.flags === MessageFlags.IsComponentsV2) {
+        const container = message.components[0];
+        if (container?.addActionRowComponents) {
+            container.addActionRowComponents(backRow);
+        }
+        return message;
+    }
+
+    // Embed-based fallback — add as a regular component row
+    return {
+        ...message,
+        components: [...(message.components || []), backRow],
+    };
+}
+
 /**
  * Resolves an item URL (icon or image) for use in CV2 components.
  * Handles both local assets and remote URLs.