chore: add AGENTS.md with LynxPrompt footer

Author: GeiserX

AGENTS.md

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+# AGENTS.md — Wayback-Diff
+
+## Project Overview
+
+Intelligent web page comparison tool with Wayback Machine support and visual regression testing.
+
+- **Repo:** [GeiserX/Wayback-Diff](https://github.com/GeiserX/Wayback-Diff)
+- **Language:** Python
+- **License:** GPL-3.0
+
+## Security
+
+> **Do not commit secrets to the repository.**
+> Use environment variables or secure vaults for credentials.
+
+---
+
+*Generated by [LynxPrompt](https://lynxprompt.com) CLI*