Add UPC support to product import, item search and UI

[mch987]

Motivation

• Allow UPC/barcode to be stored and used when importing products so scanned barcodes can prefill items and detect duplicates.
• Make UPC searchable so users can find items by barcode from the main item search flow.
• Surface UPC in the UI (create modal, edit form and import modal) to improve scanning/import UX.

Description

• Added upc to the entity API types and DTOs used by the frontend (EntityCreate, EntityUpdate, EntityOut, EntitySummary) so UPC is part of the API contract and form payloads.
• Wired product import flow so the barcode returned from product lookup is placed into the item create payload and persisted (backend maps UPC into the existing import_ref storage field to avoid ent codegen changes in this rollout).
• Extended repository search to include UPC (implemented via ImportRefContainsFold where UPC is stored) so searching by barcode will find matching items.
• Added duplicate-detection UI in the Barcode/Product Import modal that queries existing items for the scanned UPC and shows quick “Open” buttons for matches before importing a new item.
• Exposed UPC in the item create modal and item edit form and added an English locale key for the items.upc label.

Testing

• Attempted to run backend repository tests with go test ./internal/data/repo -run TestNormalizeSearchQueryIntegration, but execution did not complete in this environment (test run/timeouts and go generate failed due to external network/module fetch restrictions), so the full automated test suite was not completed.
• Verified repository changes were committed successfully (git commit completed) and performed local inspections of modified TypeScript and Vue files to ensure the new upc fields are passed through create/update flows and rendered in the UI.
• Manual smoke checks in code: ensured product import modal now queries api.items.getAll and filters by upc to display existing items (no runtime test harness was executed here).

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Codex Task