docs: replace 62 scattered/stale markdown files with two living references

Removes all tracked repo documentation (root status docs, docs/,
docs/architecture/foundation/**, docs/archive/**, docs/context/BACKEND-AUDIT.md
+ adrs, src/assets/mock/README.md) and replaces it with:

- GAPS-AND-IMPROVEMENTS.md — role-based findings (user, PO, QA, backend,
  accessibility, engineering) plus automated code-review passes over the
  storefront and backoffice, each with file:line references. Findings only,
  no fixes applied.
- BACKEND-API-REFERENCE.md — single consolidated backend contract: auth
  (both mechanisms), bootstrap, pagination/sorting/filtering conventions,
  error model, every live/mock-only endpoint with JSON examples, and the
  admin-domain DI-token seam gaps.

Open items and unresolved decisions from the deleted docs (KNOWN-ISSUES,
PRODUCT_BACKLOG, SPRINT-PLAN-NEXT, Seller-Management audits, etc.) were
harvested into the two new files before deletion, not lost.

CLAUDE.md/AGENTS.md/GEMINI.md/.claude/ and docs/context/{INDEX,LOG,
MAINTENANCE,README}.md are untouched — confirmed gitignored, never part of
git history, outside this cleanup's scope.

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

src/assets/mock/README.md

@@ -1,8 +0,0 @@
-# Mock Data Boundaries
-
-- `bootstrap/`: tenant and platform configuration only.
-- `website/`: website business/content mocks.
-- `builder/`: builder configuration editing mocks.
-- `backoffice/`: business domain data (products, categories, orders, customers).
-
-Backoffice business data must not be stored under `bootstrap/`.