Add test coverage checklist, report template, and stack matrix for ecommerce project

- Created a test coverage checklist to ensure comprehensive testing of backend and frontend components.
- Added a test report template to standardize reporting on test execution results and gaps.
- Introduced a test stack matrix to guide the selection of testing tools and frameworks for backend and frontend.
- Established a skill for repairing failing tests, including a failure triage checklist and a test repair template.
- Documented recommended MCP stack for ecommerce development with FastAPI and React/Next.js.
- Developed a detailed README outlining the project structure, agent capabilities, and recommended workflows.
- Compiled a comprehensive workflow guide detailing step-by-step commands for project setup, testing, and SEO implementation.

site-fullstack/.github/skills/ecommerce-build-from-brief/assets/build-checklist.md

@@ -0,0 +1,17 @@
+# Build Checklist
+
+Before implementation, confirm that .ai/STORE-BRIEF.md contains enough detail for:
+
+- Repo mode and current repo responsibilities.
+- Backend stack and database choice.
+- Frontend stack and rendering assumptions.
+- Storefront pages and flows.
+- Auth model and cart model.
+- Admin modules and staff roles.
+- Catalog entities and filtering model.
+- Order or lead flow.
+- Integrations and external dependencies.
+- Visual direction and asset status.
+- AGENTS.md plan.
+
+If one of these is materially missing, ask a focused follow-up question or record the implementation assumption before building.