feat(llms): convert ApiLink components to markdown links in generated .md files

[viktorkombov]

Closes #338

Improves the generated .md versions of documentation pages so they can be reliably parsed by LLMs and coding agents. First step of a broader effort to preserve all meaningful content from MDX source in the LLM-facing markdown output.

Previously <ApiLink> components were stripped entirely from .md files, losing all API identifiers and links. They are now resolved to proper markdown links using the same logic as the rendered HTML.

Changes

• stripMdxForLlms converts <ApiLink …/> to [`IgxToast`](url) (or `IgxToast` fallback when index is unavailable) instead of removing them
• platformContext option added to siteMetaIntegration / createDocsSite to supply the API index at build time
• getPlatformContext() accepts an optional explicit platform name to avoid relying on env vars
• Both docs/angular and docs/xplat pass platformContext to createDocsSite
• igniteui-astro-components pointed to local repo (pending astro-components PR merge)

Verification

• <ApiLink type="Grid" /> resolves to a working link in the generated .md
• <ApiLink type="Grid" member="rowSelection" /> resolves with correct member anchor
• <ApiLink kind="sass" module="themes" type="function-avatar-theme" /> resolves to correct Sass docs URL
• <ApiLink label="custom" type="Toast" /> uses the label override, not the auto-generated name
• <ApiLink prefixed={false} type="IgxToast" /> skips prefix prepending
• API References section entries are links, not plain inline code
• Unresolved symbols fall back to `TypeName` inline code (no broken links)
• Angular, React, WebComponents, and Blazor builds all produce correct platform-specific URLs

Checklist:

• check topic's TOC/menu and paragraph headings
• Include TOC topic labels in the topic content when it has a valuable update, is new, or is considered preview / beta
• link to other topics using ../relative/path.md
• at the References section at the end of the topic add links to topics, samples, etc
• reference API documentation instead of adding a section with API

• use valid component names - [Data] Grid, IgxSelectComponent, <igx-combo>
• use spell checker tool (VS Code, Grammarly, Microsoft Editor)
• add inline code blocks for the names of classes / tags / properties
• add language descriptor for the code blocks
• check if links function by running the check-api/mdx npm commands
• check if sample is working and fully visible in the topic
• check if sample is working and fully visible in the StackBlitz
• check if code blocks match the code in StackBlitz demo

• follow SEO guidelines to fill topic's metadata (SEO guidelines)

• do not resolve requested changes (leave that to the reviewer)