refactor: add inventory view layer

Create inventory.view.ts with UI logic extracted from commands:
- getInventoryEmbed() for inventory display
- getItemUseResultEmbed() for item use results

Updated commands with proper type safety:
- inventory.ts: add null check, convert user.id to string
- use.ts: add null check, convert user.id to string

Improves separation of concerns and type safety.

src/commands/inventory/use.ts

@@ -2,7 +2,8 @@ import { createCommand } from "@/lib/utils";
 import { SlashCommandBuilder } from "discord.js";
 import { inventoryService } from "@/modules/inventory/inventory.service";
 import { userService } from "@/modules/user/user.service";
-import { createErrorEmbed, createSuccessEmbed } from "@lib/embeds";
+import { createErrorEmbed } from "@lib/embeds";
+import { getItemUseResultEmbed } from "@/modules/inventory/inventory.view";
 import { inventory, items } from "@/db/schema";
 import { eq, and, like } from "drizzle-orm";
 import { DrizzleClient } from "@/lib/DrizzleClient";
@@ -25,9 +26,13 @@ export const use = createCommand({
 
         const itemId = interaction.options.getNumber("item", true);
         const user = await userService.getOrCreateUser(interaction.user.id, interaction.user.username);
+        if (!user) {
+            await interaction.editReply({ embeds: [createErrorEmbed("Failed to load user data.")] });
+            return;
+        }
 
         try {
-            const result = await inventoryService.useItem(user.id, itemId);
+            const result = await inventoryService.useItem(user.id.toString(), itemId);
 
             const usageData = result.usageData;
             if (usageData) {
@@ -53,11 +58,7 @@ export const use = createCommand({
                 }
             }
 
-            const embed = createSuccessEmbed(
-                result.results.map(r => `• ${r}`).join("\n"),
-                `Used ${result.usageData.effects.length > 0 ? 'Item' : 'Item'}` // Generic title, improves below
-            );
-            embed.setTitle("Item Used!");
+            const embed = getItemUseResultEmbed(result.results);
 
             await interaction.editReply({ embeds: [embed] });