docs: add advanced skills for Vitest, Pinia, and Vue built-ins

Add comprehensive reference documentation for:
- Vitest: environments, projects/workspaces, type testing, vi utilities
- Pinia: HMR, Nuxt integration, SSR setup
- Vue: built-in components (Transition, Teleport, Suspense, KeepAlive) and advanced directives

.agents/skills/vue-router-best-practices/SKILL.md

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+---
+name: vue-router-best-practices
+description: "Vue Router 4 patterns, navigation guards, route params, and route-component lifecycle interactions."
+version: 1.0.0
+license: MIT
+author: github.com/vuejs-ai
+---
+
+Vue Router best practices, common gotchas, and navigation patterns.
+
+### Navigation Guards
+- Navigating between same route with different params → See [router-beforeenter-no-param-trigger](reference/router-beforeenter-no-param-trigger.md)
+- Accessing component instance in beforeRouteEnter guard → See [router-beforerouteenter-no-this](reference/router-beforerouteenter-no-this.md)
+- Navigation guard making API calls without awaiting → See [router-guard-async-await-pattern](reference/router-guard-async-await-pattern.md)
+- Users trapped in infinite redirect loops → See [router-navigation-guard-infinite-loop](reference/router-navigation-guard-infinite-loop.md)
+- Navigation guard using deprecated next() function → See [router-navigation-guard-next-deprecated](reference/router-navigation-guard-next-deprecated.md)
+
+### Route Lifecycle
+- Stale data when navigating between same route → See [router-param-change-no-lifecycle](reference/router-param-change-no-lifecycle.md)
+- Event listeners persisting after component unmounts → See [router-simple-routing-cleanup](reference/router-simple-routing-cleanup.md)
+
+### Setup
+- Building production single-page application → See [router-use-vue-router-for-production](reference/router-use-vue-router-for-production.md)