Add AgentAudit Security Badge ✅ (#15)

## AgentAudit Security Badge

This PR adds a security badge from
[AgentAudit](https://www.agentaudit.dev), an open security registry for
AI packages.

Your package has been officially audited by AgentAudit and received a
**Safe** rating with no security findings.

🔗 [View full audit report](https://www.agentaudit.dev/skills/agentgram)

### What is AgentAudit?
AgentAudit is a transparency-first security registry that audits MCP
servers, AI skills, and agent packages. Our audits use a 3-pass
methodology (understand → detect → classify) to minimize false positives
while catching real vulnerabilities.

Author: starbuck100

README.md

@@ -1,5 +1,8 @@
 # AgentGram Python SDK
 
+[![AgentAudit Security](https://img.shields.io/badge/AgentAudit-Safe-brightgreen?logo=data:image/svg%2Bxml;base64,PHN2ZyB4bWxucz0iaHR0cDovL3d3dy53My5vcmcvMjAwMC9zdmciIHZpZXdCb3g9IjAgMCAyNCAyNCI+PHBhdGggZmlsbD0id2hpdGUiIGQ9Ik0xMiAxTDMgNXY2YzAgNS41NSAzLjg0IDEwLjc0IDkgMTIgNS4xNi0xLjI2IDktNi40NSA5LTEyVjVsLTktNHoiLz48L3N2Zz4=)](https://www.agentaudit.dev/skills/agentgram)
+
+
 [![PyPI version](https://badge.fury.io/py/agentgram.svg)](https://badge.fury.io/py/agentgram)
 [![Python 3.9+](https://img.shields.io/badge/python-3.9+-blue.svg)](https://www.python.org/downloads/)
 [![License: MIT](https://img.shields.io/badge/License-MIT-yellow.svg)](https://opensource.org/licenses/MIT)