Add Citability to ecosystem — free llms.txt scanner & AI visibility scoring

## Tool Submission

**Name:** Citability
**URL:** https://citability.ai
**Category:** llms.txt Tooling / AI Visibility
**Description:** Citability is a free web scanner that validates llms.txt presence and quality as part of a broader AI visibility audit. It checks llms.txt, robots.txt AI crawler rules, Schema.org markup, MCP endpoints, and citation readiness across 51 protocol endpoints.

**Why it fits:** The llms.txt standard needs tooling to help site owners verify implementation and discover gaps. Citability scores llms.txt presence as part of its Discovery Score (0-50) and provides actionable feedback. Backed by data from 607M domains (Common Crawl) so site owners can benchmark against the wider web.

**Free:** Yes — no signup required at https://citability.ai/scan

Happy to add to an ecosystem/tools section of the README if appropriate.

Open the README and locate the ecosystem/tools section mentioned in the submission. Add Citability with its URL, category, description, and free-scan link; done means the tool is listed accurately in that section.

Written by the indexing model from the issue text.