Expand README and npm metadata for discoverability

[woksin]

What changed

• README.md — expanded the short description into a proper landing page: a positioning line (React components for CQRS and event-sourced applications built with Cratis Arc), an install section with a minimal setup snippet, a named component inventory (CommandDialog, CommandForm, DataPage, DataTables, Dialogs, Chat, SchemaEditor, TimeMachine, PivotViewer, and more), a clear note on the library's MIT license versus PrimeReact 11's own terms (linking the package README's licensing section), and a Cratis ecosystem section cross-linking Chronicle, Arc, CLI + Workbench, and supporting projects.
• Source/package.json — filled the empty npm description, added keywords (react, react-components, component-library, cqrs, event-sourcing, cratis, arc, chronicle, commands, queries, data-table, forms, typescript), and added a homepage pointing at the docs site.
• Source/README.md (npm-rendered) — rewrote the first paragraph to say what the library is for (CQRS, event sourcing, Arc proxies) and added a short "Part of the Cratis ecosystem" section linking Arc, Chronicle, Fundamentals, cratis.io, and Discord.
• Documentation/index.mdx — added "CQRS and event-sourced applications" to the frontmatter description and a "Related" card grid cross-linking Arc, Chronicle, and the CLI.

Why

Better discoverability: the package currently publishes with an empty npm description and no keywords, and the README does not say what the library is for or how it relates to the rest of the Cratis stack. This gives searchers (npm, GitHub, docs site) accurate category terms and ecosystem cross-links, with factual wording only.

Verification

• Source/package.json parses as valid JSON.
• markdownlint-cli2 passes on the changed files (the one remaining MD040 finding in Source/README.md pre-exists this change).
• Relative link anchors (#licensing, #available-subpath-exports) verified against the package README headings; the "Related" cards reuse icon names already used in this docs file.