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-store-evolution/assets/extension-checklist.md

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+# Extension Checklist
+
+- What already exists in the storefront.
+- What already exists in the admin panel or back office.
+- Current auth model and role system.
+- Current cart behavior and checkout assumptions.
+- Current backend modules, migrations, and API style.
+- Current design system or UI conventions.
+- Which parts can be extended safely versus which parts need refactoring.
+- Which gaps must be documented in AGENTS.md.

site-fullstack/.github/skills/ecommerce-store-evolution/assets/rollout-plan-template.md

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+# Rollout Plan Template
+
+## Goal
+- What business or UX capability is being added or changed.
+
+## Existing constraints
+- Current architecture limits.
+- Current data contract limits.
+
+## Change plan
+- Backend changes.
+- Frontend storefront changes.
+- Admin or back office changes.
+- Migration or seed changes.
+
+## Verification
+- Manual flows to verify.
+- High-risk regressions to watch.