Add skill files (`SKILL.md`) for AI-assisted development

[georgianastasov]

Is your feature request related to a problem? Please describe.

There are no domain-specific Copilot skill files in the Ignite UI Blazor repository. When developers ask Copilot to implement features using Ignite UI Blazor - grids, charts, form controls, theming - the responses lack awareness of library-specific APIs, component setup requirements, and known gotchas.

This leads to incorrect or incomplete code that requires manual correction.

Describe the solution you'd like

Add a skills directory containing SKILL.md files for each major domain:

igniteui-blazor-components

• SKILL.md — UI components: form controls, layout, data display, feedback/overlays, charts

igniteui-blazor-grids

• SKILL.md — Data grids: column config, sorting, filtering, editing, paging, remote data, Tree Grid, Hierarchical Grid, Pivot Grid, state persistence

igniteui-blazor-theming

• SKILL.md — Theming and styling, including MCP server setup

Each skill file teaches Copilot how to correctly use that area of the library by providing accurate API usage, required imports/setup, and common patterns verified against the actual library.

Describe alternatives you've considered

The skill file pattern, already in use for the Angular repo, allows Copilot to load only the relevant domain knowledge on demand.