Add llms.txt and machine-readable EloqKV source map

[liunyl]

Epic: #47

Background

llms.txt is not a ranking prerequisite, but it can serve as a useful machine-readable map for EloqKV definitions, docs, benchmark pages, and articles.

Tasks

• Add /llms.txt with concise EloqKV summary and links to canonical sources.
• Include product page, docs, cost calculator, benchmark article/page, migration guide, FAQ hub, GitHub repo, and whitepaper HTML page.
• Keep claims conservative and aligned with visible site content.
• Ensure the file is deployed at the site root.

Acceptance criteria

• /llms.txt is publicly accessible.
• It points only to canonical, maintained EloqKV URLs.
• It does not introduce claims absent from the website.