Add file_count and files_total_size to item API responses, computed
via batch query on item_files table (no migration needed).
- Add BatchGetFileStats() to audit_queries.go (follows BatchCheckBOM pattern)
- Add file stats to ItemResponse, HandleListItems, HandleGetItem, HandleGetItemByUUID
- Add 'Files' column to ItemTable (default visible in vertical mode)
- Add has_files computed field to audit completeness scoring (weight 1 for manufactured)
- New /audit page with completeness scoring engine
- Weighted scoring by sourcing type (purchased vs manufactured)
- Batch DB queries for items+properties, BOM existence, project codes
- API endpoints: GET /api/audit/completeness, GET /api/audit/completeness/{pn}
- Audit UI: tier summary bar, filterable table, split-panel inline editing
- Create item form now shows category-specific property fields on category select
- Properties collected and submitted with item creation
