feat(catalog): full vehicle selector flow in brand catalog

Brand catalog now follows the same navigation as the regular catalog:
1. Brands -> 2. Models -> 3. Years -> 4. Engines -> 5. Categories -> 6. Parts

Backend:
- Add /mye-parts endpoint for MYE-specific parts with category filter
- Uses existing /models, /years, /engines, /categories endpoints

Frontend:
- Complete rewrite of brand-catalog.js with breadcrumb navigation
- State machine: brands -> models -> years -> engines -> categories -> parts
- Search and pagination preserved at parts level
- Breadcrumb allows jumping back to any previous step

pos/blueprints/catalog_bp.py

@@ -763,3 +763,107 @@ def brand_parts():
         finally:
             cur.close()
     return _with_conns(_query)
+
+
+@catalog_bp.route('/mye-parts', methods=['GET'])
+@require_auth('catalog.view')
+def mye_parts():
+    """Return parts for a specific MYE + category (brand-catalog flow).
+    
+    Skips the group/subgroup level and goes directly from category to parts.
+    """
+    mye_id = request.args.get('mye_id', type=int)
+    category_id = request.args.get('category_id', type=int)
+    search = request.args.get('search', '').strip()
+    limit = request.args.get('limit', 50, type=int)
+    offset = request.args.get('offset', 0, type=int)
+
+    if not mye_id:
+        return jsonify({'error': 'mye_id required'}), 400
+
+    def _query(master, tenant, branch_id):
+        cur = master.cursor()
+        try:
+            # Build dynamic filters
+            cat_filter = ""
+            search_filter = ""
+            params = [mye_id]
+
+            if category_id:
+                cat_filter = "AND pc.id_part_category = %s"
+                params.append(category_id)
+
+            if search:
+                search_filter = "AND (p.oem_part_number ILIKE %s OR COALESCE(NULLIF(p.name_es, ''), p.name_part) ILIKE %s)"
+                like_term = f"%{search}%"
+                params.extend([like_term, like_term])
+
+            # Get parts
+            query_params = list(params)
+            cur.execute(f"""
+                SELECT DISTINCT p.id_part, p.oem_part_number,
+                       COALESCE(NULLIF(p.name_es, ''), p.name_part) as name,
+                       pg.id_part_group, pg.name_part_group,
+                       pc.id_part_category, pc.name_part_category
+                FROM vehicle_parts vp
+                JOIN parts p ON p.id_part = vp.part_id
+                JOIN part_groups pg ON pg.id_part_group = p.group_id
+                JOIN part_categories pc ON pc.id_part_category = pg.category_id
+                WHERE vp.model_year_engine_id = %s
+                {cat_filter}
+                {search_filter}
+                ORDER BY p.id_part
+                LIMIT %s OFFSET %s
+            """, query_params + [limit, offset])
+
+            part_rows = cur.fetchall()
+            part_ids = [r[0] for r in part_rows]
+
+            # Count total
+            cur.execute(f"""
+                SELECT COUNT(DISTINCT p.id_part)
+                FROM vehicle_parts vp
+                JOIN parts p ON p.id_part = vp.part_id
+                JOIN part_groups pg ON pg.id_part_group = p.group_id
+                JOIN part_categories pc ON pc.id_part_category = pg.category_id
+                WHERE vp.model_year_engine_id = %s
+                {cat_filter}
+                {search_filter}
+            """, params)
+            total = cur.fetchone()[0]
+
+            # Enrich with local stock if available
+            local_stock = {}
+            if tenant and part_ids:
+                try:
+                    from services.catalog_service import _get_local_stock_bulk
+                    local_stock = _get_local_stock_bulk(tenant, part_ids)
+                except Exception:
+                    pass
+
+            items = []
+            for r in part_rows:
+                part_id = r[0]
+                stock_info = local_stock.get(part_id, {})
+                items.append({
+                    'id': part_id,
+                    'oem_part_number': r[1],
+                    'name': r[2],
+                    'group': {'id': r[3], 'name': r[4]},
+                    'category': {'id': r[5], 'name': r[6]},
+                    'local_stock': stock_info.get('stock', 0),
+                    'local_price': stock_info.get('price', None),
+                })
+
+            return jsonify({
+                'mye_id': mye_id,
+                'category_id': category_id,
+                'search': search,
+                'items': items,
+                'total': total,
+                'limit': limit,
+                'offset': offset,
+            })
+        finally:
+            cur.close()
+    return _with_conns(_query)