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/prompts/ecommerce-build-from-brief.prompt.md

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+name: "Ecommerce Build From Brief"
+description: "Build an ecommerce project from .ai/STORE-BRIEF.md, creating AGENTS.md first and then implementing backend, storefront, and admin scope."
+agent: "shop-fullstack-fastapi-react"
+Build the project from the normalized brief.
+
+Requirements for this run:
+- Read .ai/STORE-BRIEF.md first.
+- If .ai/STORE-BRIEF.md is missing, create it first or ask to run the brief-preparation workflow.
+- Create or update AGENTS.md before application code.
+- Before serious backend or frontend edits, create a timestamped snapshot in .backup/ and do not modify older backup entries.
+- Build with a scalable architecture where models, services, config, routing, components, features, and api layers live in their own folders.
+- Implement backend, storefront, and admin panel or back office according to the brief.
+- Preserve mobile-first UX, animation quality, and asset handling.