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-test-implementation.prompt.md

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+name: "Ecommerce Test Implementation"
+description: "Write backend and frontend automated tests, run them, and create .ai/TEST-REPORT.md with results and gaps."
+agent: "shop-fullstack-fastapi-react"
+Create or extend automated tests for the project.
+
+Requirements for this run:
+- Inspect the current backend and frontend test stack first.
+- Add meaningful backend and frontend tests for the relevant flows.
+- Before serious backend or frontend edits, create a timestamped snapshot in .backup/ and keep older backup entries immutable.
+- Run the relevant test suites.
+- Create or update .ai/TEST-REPORT.md.
+- If failures remain, clearly say that the next step is to run Ecommerce Test Repair.