Add AI-search friendly project context files and crawlable docs entry points

[httpdss]

Summary

Add machine-readable and AI-search-friendly entry points so agents and AI search tools can quickly understand StructKit.

Scope

• Add or publish an llms.txt equivalent for the documentation site if the site build supports it.
• Add a concise project overview markdown page with: what StructKit is, who it is for, install commands, key features, examples, comparison links, and repository link.
• Ensure docs pages are crawlable and linked from the homepage/docs index.
• Add schema/metadata where the docs site supports it.

Why this matters

AI assistants and answer engines increasingly summarize and recommend developer tools. StructKit should be easy to parse, cite, and compare.

Acceptance criteria

• AI-friendly overview content is present in the repo/docs site source.
• The overview links to quickstart, examples, MCP docs, and comparison docs.
• Main README/docs index link to this content where appropriate.
• Content avoids hype and states concrete capabilities.