Updates https://github.com/coder/coder/issues/18779
A separate PR will update dependant modules `goose` and `aider`.
## Description
* Adds `subdomain` argument to `agentapi` module
* Updates `agentapi` module to set `AGENTAPI_CHAT_BASE_PATH` to an
autogenerated path if `var.subdomain = false`
* Updates default `agentapi` version to `v0.3.3` to support running
without subdomain
## Type of Change
- [ ] New module
- [ ] Bug fix
- [x] Feature/enhancement
- [ ] Documentation
- [ ] Other
## Testing & Validation
- [X] Tests pass (`bun test`)
- [X] Code formatted (`bun run fmt`)
- [x] Changes tested locally
## Related Issues
- https://github.com/coder/coder/issues/18779
The agentapi module is a building block for modules that need to run an
agentapi server. It's not meant for end users of Coder.
The agentapi-specific logic is mostly extracted from [the claude-code
module](c0f2d945c5/registry/coder/modules/claude-code).
You can see this module in action in [the goose 2.0
PR](https://github.com/coder/registry/pull/178).
