chore: remove deprecated instruction files

- Remove 11 deprecated instruction files migrated to Agent Skills
- Universal instruction files remain as custom instructions

Release v0.0.3: Fix README formatting

Release v0.0.2: Agent Skills Migration

Implemented 11 modular Agent Skills following the Agent Skills specification:
- javascript-typescript-standards (ES2022, Node.js)
- vue-development (Vue 3 Composition API)
- nuxt-development (Nuxt 3, SSR/SSG)
- css-standards (CSS organization)
- tailwind-css (Tailwind v4+)
- html-standards (Semantic markup)
- csharp-standards (C# conventions)
- dotnet-development (.NET architecture)
- markdown-standards (Documentation)
- testing-tdd (TDD workflow)
- commit-conventions (Conventional Commits)

- ~70% reduction in baseline token usage
- Dynamic loading of skills when relevant
- Progressive disclosure pattern
- Better discoverability
- Executable scripts included

- Agent Skills README with comprehensive overview
- Migration guide explaining rationale
- Updated main README
- CHANGELOG.md for version tracking

See CHANGELOG.md for full details.

chore(readme): remove outdated GitHub Copilot instructions