Converts BB command argument definitions into Peri schemas suitable for Anubis.Server.Frame.register_tool/3.

Anubis takes the Peri schema we hand it, validates incoming tool calls against it, and re-renders it as JSON Schema on the wire. So one conversion suffices for both validation and discovery.

BB types map to Peri types as follows:

:integer | :pos_integer | :non_neg_integer -> :integer
:float | :number                           -> :float
:string                                    -> :string
:boolean                                   -> :boolean
:atom                                      -> :string
{:in, values}                              -> {:enum, values}
:map | {:map, fields}                      -> :map
:keyword_list                              -> :keyword
{:list, inner}                             -> {:list, :any}
:any                                       -> :any
module / unknown                           -> :any

JSON has no atoms, so an :atom or {:in, [:a, :b]} argument is validated as a string and converted back to an atom by to_goal/2 on the way to the command. An enum of atoms only ever admits the declared members, so those convert against the declared list; a bare :atom has no declared list and falls back to String.to_existing_atom/1, leaving the client's string in place when no such atom exists rather than interning whatever was sent.