Add 2 open-source GEO utilities + ThatDevPro reference library

[Janady13]

Adds 3 entries across two relevant sections:

Tools & Software → Utilities & Generators (2 new open-source MIT-licensed tools):

• aio-surfaces — Python toolkit that generates the four AI-citation surfaces (llms.txt, aeo.json, entity.json, brand.json) from a single typed site config. Used in production on thatdevpro.com.
• seo-sidecar — FastAPI + nginx SSI sidecar for injecting fresh Schema.org JSON-LD into nginx-served sites without redeploys. MIT licensed.

Technical Documentation → llms.txt Protocol → Adoption & Directories (1 new reference):

• ThatDevPro Reference Library — 26 canonical reference pages covering every crawler signal a website emits. HTML meta (15 pages: viewport, theme-color, refresh, referrer, keywords, generator, content-language, color-scheme, charset, robots, copyright, author, Open Graph, Twitter Cards) + HTTP status codes (2xx/3xx/4xx/5xx) + HTTP headers (caching, content, CORS, performance, rate-control, request, security, SEO). Cross-linked from a deployed /llms.txt + /llms-full.txt pair.

All three additions are real production artifacts, not scaffold or demo projects. The two utilities are public on GitHub under MIT license; the reference library is the primary documentation surface for ThatDevPro's GEO/AEO/SEO practice.