docs: Storefront audit for market.com/seller.market.com compatibility

Audit only, no code changed - facts gathered by reading current
source (routes, containers, header/footer, SeoService), not assumed.
Covers Homepage, Categories, Products, Search, Favorites, Cart,
Checkout, Reviews, SEO, Breadcrumbs, Header, Footer.

Core finding: tenant resolution is already entirely backend-side by
request Host (ADR-001) - the frontend just consumes whatever bootstrap
comes back for whatever hostname it's running on. A seller subdomain
is architecturally closer to already working than any part of the
Backoffice audit found; the real gaps are all about whether the
*data* rendered carries a seller-aware value, not about routing/
hosting.

Key findings:
- Canonical URLs already correct today - SeoService.siteUrl derives
  from location.origin dynamically, not hardcoded. Nothing to change.
- Header/Footer/SEO branding all read through one shared facade
  (UiRuntimeFacade.reloadFromBootstrap()) - a single future injection
  point that would cascade to all three for free, rather than three
  separate fixes.
- SeoService.setItemMeta() (per-product OG/canonical tags) is defined
  but never called anywhere in the codebase today - a pre-existing
  dead hook, unrelated to seller-scoping but blocking any future
  per-product/per-seller SEO work until wired.
- No dedicated breadcrumb component/service exists anywhere in the
  storefront - the only breadcrumb logic in the app is one local
  signal in catalog-container.component.ts.
- Checkout is not a separate route - it's an inline popup flow in
  cart.component.ts, with no multi-vendor/multi-seller cart concept
  at all. This is where Checkout Modes and Unified/Split Orders (both
  marked Future in Seller-Management.md) would actually need to land.
- Structured data (JSON-LD) and sitemap generation don't exist for
  anyone today, marketplace or seller - net-new work either way, not
  seller-specific gaps.
- One pre-existing, unrelated issue noted in passing: og:locale is
  hardcoded 'ru_RU' in SeoService - flagged, not fixed (out of scope).

Linked from docs/architecture/foundation/README.md alongside the
other Seller Management docs.

docs/architecture/foundation/README.md

@@ -55,6 +55,7 @@ It is a platform runtime that must support unlimited tenants from one Angular ap
 - [Seller-Management-Domain-Models.md](Seller-Management-Domain-Models.md) — typed models, optional sellerId fields
 - [Seller-Management-UX-Review.md](Seller-Management-UX-Review.md) — UX/accessibility review of the Phase 1 UI
 - [Seller-Management-Backoffice-Readiness-Audit.md](Seller-Management-Backoffice-Readiness-Audit.md) — per-module scoping/permissions readiness audit
+- [Seller-Management-Storefront-Audit.md](Seller-Management-Storefront-Audit.md) — `market.com`/`seller.market.com` storefront readiness audit
 
 ### Engineering Rule Documents