fix breadcrumb styling: semantic markup, chevron separators, mobile sizing

Rewrite breadcrumb as semantic ol/li with aria-current="page", CSS
chevron separators, 0.875em font size, and ellipsis truncation on
mobile for long product names.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

PROGRESS.md

@@ -41,7 +41,8 @@ Issues found during hands-on testing of the deployed prod site on mobile and des
 - [x] Product card second image: swipe to reveal on mobile (currently hover-only)
 
 ### Product detail page
-- [ ] Product category breadcrumbs look bad — review styling/layout
+- [x] PDP image gallery: scroll-snap carousel with dots (mobile), thumbnails + arrows + lightbox (desktop)
+- [x] Product category breadcrumbs look bad — review styling/layout
 - [ ] Quantity selector on product page doesn't work
 - [ ] Trust badges: two different tick icons, should use sentence case not title case
 - [ ] Real product variants need testing and refinement with live data
@@ -303,7 +304,8 @@ See: [docs/plans/page-builder.md](docs/plans/page-builder.md) for design
 | PageSpeed CI | 516d0d0 | `mix lighthouse` task, prod asset build, gzip, 99-100 mobile scores |
 | Observability | eaa4bbb | LiveDashboard in prod, ErrorTracker, JSON logging, Oban/LV metrics, os_mon |
 | Hosting & deployment | — | Alpine Docker, Fly.io, health check, release path fixes |
-| CI pipeline | — | mix ci/precommit aliases, credo, dialyzer, 612 tests |
+| PDP image gallery | 8445e9e | Scroll-snap carousel, dots, thumbnails, arrows, lightbox, 9 tests |
+| CI pipeline | — | mix ci/precommit aliases, credo, dialyzer, 621 tests |
 | Default content pages | 5a43cfc | Generic Content LiveView, delivery/privacy/terms pages, 10 tests |
 | Transactional emails | — | Plain text order confirmation + shipping notification, 10 tests |
 | Printify order submission & fulfilment | — | Submit, track, webhooks, polling, admin UI, 33 tests |