Support optional parameters in proxy mode

[k255]

Description

While registering shell scripts as MCP tools is a great feature in its current implementation all parameters are marked as required.
Having the option to mark some parameters as optional greatly improves flexibility.

With the proposed change, to mark given parameter as optional, you just wrap it in brackets, e.g.:

{
  "add_operation": {
    "command": "echo \"$msg$a + $b = $(($a+$b))\"",
    "description": "Adds a and b with optional result msg",
    "parameters": "a:int,b:int,[msg:string]",
    "script": ""
  }
}

Type of change

Please delete options that are not relevant.

• New feature (non-breaking change which adds functionality)

How Has This Been Tested?

This was tested with provided 'mcp web' interface

Checklist:

• My code follows the style guidelines of this project
• I have performed a self-review of my own code
• I have commented my code, particularly in hard-to-understand areas
• I have made corresponding changes to the documentation
• My changes generate no new warnings