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-code-review/assets/severity-rubric.md

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+# Severity Rubric
+
+## Critical
+- Likely to cause broken behavior, data loss, security issues, or severe production instability.
+- Major architecture flaw affecting core flows.
+
+## High
+- Strong risk of bugs, regressions, maintainability collapse, or significant performance issues.
+- Serious mismatch with configured quality rules.
+
+## Medium
+- Clear quality issue or missed optimization that should be fixed, but not an immediate release blocker.
+
+## Low
+- Smaller maintainability issues, cleanup, or polish items.
+
+## Finding format
+- Severity
+- Area
+- Location
+- Problem
+- Why it matters
+- Recommended fix
+- Confidence or assumptions when relevant