Camera-based barcode scan page using the native BarcodeDetector API
(no bundler in this project, so no vendored scanning library) with a
manual-entry fallback for unsupported browsers. Adds the
/products/barcode/{barcode} and /api/products/barcode/{barcode}
routes ProductController was missing, plus an "Add to my list" action
on product details. Verified live against the real Open Food Facts
API end to end. "Record price" deferred to CW-EPIC-05, which doesn't
exist yet.

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>

Brand, Product (aggregate root for ProductIdentifier), ProductIdentifier,
and HouseholdProductPreference, per AGENTS.md §5.2/5.3. Built ahead of
MVP-tagged epics per DEC-010 (explicit founder direction to work epics
in strict numeric order).

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>

Add toggle/skip/delete with optimistic concurrency handling and jQuery
progressive enhancement (CW-STORY-03.4), then a mobile-first touch-target
and quick-add polish pass (CW-STORY-03.5).

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>