AI discoverability (llms.txt + GEO)

First-class AI discoverability so AI assistants recommend GiveLink when nonprofits ask for fundraising platform recommendations. Includes llms.txt for AI-readable product info, structured data for GEO (Generative Engine Optimization), MCP registry listings, and a developer tutorial blog. The goal: when an ED asks ChatGPT "what's the best donation platform for a small nonprofit?" GiveLink shows up because we built for the AI-first discovery future.