Created 8 helper functions for common inventory operations:
1. get_inventory_details() - Full inventory list with denormalized data
2. get_expiring_items(days) - Items expiring within N days
3. get_items_by_tag(tag_name) - Filter by tag
4. get_low_stock_items(threshold) - Items below quantity threshold
5. update_item_quantity() - Consume/restock with optional auto-delete
6. get_inventory_stats() - Dashboard statistics
7. search_inventory() - Full-text search across items and products
All functions include comments and are optimized for frontend queries.
Closes#15
