feat: add support for custom agents from config directory

[jingkaihe]

Link to the discussion - #163

This PR added support for loading custom agents from <config_home>/agents/*.toml

e.g. I added

# Schema defined in agent_schema.py
# https://github.com/jingkaihe/kodelet

identity = "kodelet"
name = "Kodelet"
short_name = "kodelet"
url = "https://github.com/jingkaihe/kodelet"
protocol = "acp"
author_name = "Jingkai He"
author_url = "https://github.com/jingkaihe/kodelet"
publisher_name = "Jingkai He"
publisher_url = "https://github.com/jingkaihe/kodelet"
type = "coding"
description = "Kodelet is a lightweight agentic SWE Agent. It runs as an interactive CLI tool in your terminal. It is capable of peforming software engineering and production operating tasks."
tags = []
run_command."*" = "kodelet acp"

help = '''
...

into ~/.config/toad/agents/kodelet.toml, agents become available from the tui on toad launch:

This allows me to launch custom agent via toad serve which otherwise isn't available.

[willmcgugan]

The toad acp subcommand has a --serve switch.

This change is necessary, but I'd want to add validation. At the moment, if the format is wrong it will break the UI.

I was planning to do validation with typeguard, and add some UI to report any errors

[jingkaihe]

yep running into error today as I missed a few lines copying config from one server to another and got follow:

it was pretty clear what went wrong though

[jingkaihe]

@willmcgugan I have added the schema validation, let me know what you think

Disclaimer: the changes are made with opus 4.5, driven by myself

[tidux]

This would be very nice to have for ZeroClaw users, especially those running local models.

[tidux]

ZeroClaw now supports session/resume in master so it would be nice to have it available as a "real" Agent rather than toad acp.

[willmcgugan]

@tidux Suggest you open a PR. Or a discussion.

[tidux]

@willmcgugan this custom agent PR represents my preferred strategy at this time. If there's some reason you're not merging it you should say so and I can raise a PR with a different one.