feat: add cart page, cart drawer, and shared cart infrastructure

- Cart context with pure functions for add/remove/update/hydrate
- Price formatting via ex_money (replaces all float division)
- CartHook on_mount with attach_hook for shared event handlers
  (open/close drawer, remove item, PubSub sync)
- Accessible cart drawer with focus trap, scroll lock, aria-live
- Cart page with increment/decrement quantity controls
- Preview mode cart drawer support in theme editor
- Cart persistence to session via JS hook + API endpoint
- 19 tests covering all Cart pure functions

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

PROGRESS.md

@@ -10,15 +10,16 @@
 - Shop pages (home, collections, products, cart, about, contact)
 - Mobile-first design with bottom navigation
 - 100% PageSpeed score
+- Variant selector with color swatches and size buttons
 
 **In Progress:**
-- Products context with provider integration (wired to shop views, variant selector next)
+- Session-based cart
 
 ## Next Up
 
-1. **Variant Selector Component** - Size/colour picker on product pages
-2. **Session-based Cart** - Real cart with actual variants
-3. **Stripe Checkout Integration** - Payment processing
+1. **Session-based Cart** - Real cart with actual variants
+2. **Stripe Checkout Integration** - Payment processing
+3. **Orders & Fulfillment** - Submit orders to Printify
 
 ---
 
@@ -52,9 +53,8 @@
 See: [docs/plans/image-optimization.md](docs/plans/image-optimization.md) for implementation details
 
 ### Products & Provider Integration
-**Status:** In Progress
+**Status:** Complete
 
-#### Completed
 - [x] Products context with schemas (c5c06d9)
 - [x] Provider abstraction layer
 - [x] Printify client integration
@@ -64,21 +64,16 @@ See: [docs/plans/image-optimization.md](docs/plans/image-optimization.md) for im
 - [x] Slug-based fallback matching for changed provider IDs
 - [x] Printify webhook endpoint with HMAC verification (a9c15ea)
   - Note: Printify only supports `product:deleted` and `product:publish:*` events (no `product:updated`)
-
-#### Remaining Tasks
-- [ ] Add variant selector component (~2hr)
-
-#### Recently Completed
-- [x] Product image download pipeline
+- [x] Product image download pipeline (1b49b47)
   - Downloads Printify CDN images via ImageDownloadWorker
   - Processes through Media pipeline (WebP conversion, AVIF/WebP variants)
-  - PreviewData uses local images for responsive `<picture>` elements
-  - sync_product_images preserves image_id when URL unchanged
   - Startup recovery and `mix simpleshop.download_images` backfill
-- [x] Wire shop LiveViews to Products context
-  - PreviewData now uses real products when available
-  - Fixed Printify image sync (position was string, not integer)
-  - Improved category extraction from Printify tags
+- [x] Variant selector component (880e7a2)
+  - Color swatches with hex colors, size buttons
+  - Fixed Printify options parsing (Color/Size swap bug)
+  - Filters to only published variants (not full catalog)
+  - Price updates on variant change
+  - Startup recovery for stale sync status
 
 #### Future Enhancements (post-MVP)
 - [ ] Pre-checkout variant validation (verify availability before order)
@@ -124,9 +119,12 @@ See: [docs/plans/page-builder.md](docs/plans/page-builder.md) for design
 
 | Feature | Commit | Notes |
 |---------|--------|-------|
+| Variant selector | 880e7a2 | Color swatches, size buttons, price updates |
+| Product image download | 1b49b47 | PageSpeed 100% with local images |
+| Wire shop to real data | c818d03 | PreviewData uses Products context |
+| Printify webhooks | a9c15ea | Deletion + publish events |
 | Products context Phase 1 | c5c06d9 | Schemas, provider abstraction |
 | Admin provider setup UI | 5b736b9 | Connect, test, sync with pagination |
-| Printify webhooks | a9c15ea | Deletion + publish events (no update event available) |
 | Oban Lifeline plugin | c1e1988 | Rescue orphaned jobs |
 | Image optimization | Multiple | Full pipeline complete |
 | Self-hosted fonts | - | 10 typefaces, 728KB |