feat(mcp): Add TCP transport

[Snider]

Parent: #118

Complexity: Low - Similar to socket but simpler

Task

Add TCP transport for network MCP connections.

Implementation

// pkg/mcp/transport_tcp.go

type TCPTransport struct {
    addr     string
    listener net.Listener
}

func NewTCPTransport(addr string) (*TCPTransport, error) {
    listener, err := net.Listen("tcp", addr)
    if err != nil {
        return nil, err
    }
    return &TCPTransport{addr: addr, listener: listener}, nil
}

Configuration

• Default: 127.0.0.1:9100 (localhost only)
• Configurable via MCP_ADDR env var
• Consider TLS for non-localhost

Security Considerations

• Default to localhost binding
• Warn if binding to 0.0.0.0
• Future: mTLS support

Acceptance Criteria

• TCP listener with configurable address
• Localhost-only by default
• Multiple concurrent connections
• Graceful shutdown