docs: add Smithery backlink badge to README

- Added official Smithery verification badge to badge row
- Links to https://smithery.ai/servers/synapselayer/synapse-protocol
- Improves distribution readiness and verification score
- No business logic changes

Author: SynapseLayer

README.md

@@ -13,6 +13,7 @@ Synapse Layer is open-source persistent memory infrastructure for AI agents and
 [![Downloads](https://img.shields.io/pypi/dm/synapse-layer)](https://pypi.org/project/synapse-layer/)
 [![MCP Compatible](https://img.shields.io/badge/MCP-Compatible-6B4FBB)](https://modelcontextprotocol.io)
 [![License: Apache-2.0](https://img.shields.io/badge/License-Apache--2.0-blue.svg)](LICENSE)
+[![Smithery](https://smithery.ai/badge/synapselayer/synapse-protocol)](https://smithery.ai/servers/synapselayer/synapse-protocol)
 
 [Website](https://synapselayer.org) · [Docs](https://forge.synapselayer.org/docs) · [PyPI](https://pypi.org/project/synapse-layer/) · [Forge](https://forge.synapselayer.org)