Add IKEA furniture catalog with 41 items and tabbed browse UI

- Create data/ikea-catalog.json with 41 curated IKEA items across 23 series
  (KALLAX, BILLY, MALM, PAX, HEMNES, LACK, etc.) with verified dimensions
- Add source tabs (All/Standard/IKEA) to catalog panel for filtering
- Add IKEA series filter bar when viewing IKEA items
- Add IKEA badge and series label on item cards
- Add mergeCatalog() to renderer for loading additional catalog files
- Add scripts/import-ikea-hf.js for importing from HuggingFace dataset

src/renderer.js

@@ -120,6 +120,37 @@ export class HouseRenderer {
     }
   }
 
+  async mergeCatalog(url) {
+    try {
+      const res = await fetch(url);
+      if (!res.ok) throw new Error(`Failed to load catalog: ${res.status} ${res.statusText}`);
+      const extra = await res.json();
+      if (!this.catalogData) {
+        return this.loadCatalog(url);
+      }
+      // Merge categories
+      for (const cat of extra.categories || []) {
+        if (!this.catalogData.categories.includes(cat)) {
+          this.catalogData.categories.push(cat);
+        }
+      }
+      // Merge items, avoiding duplicates by id
+      for (const item of extra.items || []) {
+        if (!this._catalogIndex.has(item.id)) {
+          this.catalogData.items.push(item);
+          this._catalogIndex.set(item.id, item);
+        }
+      }
+      // Store extra catalog for tabbed access
+      if (!this._extraCatalogs) this._extraCatalogs = [];
+      this._extraCatalogs.push(extra);
+      return extra;
+    } catch (err) {
+      this._emitError('mergeCatalog', err);
+      throw err;
+    }
+  }
+
   async loadDesign(url) {
     try {
       const res = await fetch(url);