inventory: barcode scanner in Add-item dialog

Add a camera barcode/QR scanner (components/scan/barcode-scanner.tsx,
@zxing/browser lazy-loaded) and a Barcode/NDC field to the pharmacy
Add-item dialog. Scanning a GS1 DataMatrix auto-fills expiry (AI 17) and
lot (AI 10 -> notes), with the GTIN (AI 01) as the barcode; plain 1D
barcodes drop straight into the field. Persists a nullable inventory
barcode column (migration 0036) through the type/validation/service, and
surfaces it on the item detail. i18n added to all locales.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

frontend/package.json

@@ -34,6 +34,7 @@
     "@visx/scale": "^4.0.1-alpha.0",
     "@visx/shape": "^4.0.1-alpha.0",
     "@xyflow/react": "^12.10.2",
+    "@zxing/browser": "^0.2.1",
     "ai": "^6.0.193",
     "ansi-to-react": "^6.2.6",
     "better-auth": "^1.6.13",