Summary

Add initial foundation for AGNTCY Identity support to mcpd, allowing MCP servers to prepare for future identity features.

Problem

MCP servers currently have no identity mechanism. When multiple servers are exposed, there's no way to prepare for tracking or access control.

Solution

This PR (#154) implements key generation and storage infrastructure:

What's Implemented:

• mcpd identity generate command creates ED25519 key pairs
• Keys stored in config directory
• Config field to specify identity ID

What's NOT Implemented:

• Headers are not sent in requests
• No signature creation or verification
• No access control enforcement
• No credential operations

This is foundation work only. Full identity implementation would require protocol-level changes.

Implementation Details

See PR #154 for the current implementation that generates and stores keys for future use.