move `--type` arg from command line to config

alternatively, we could move everything to config files and use command line for overriding config entries. Requiring that certain arguments be provided via the command line is confusing, at least for me.

The issue names only the `--type` command-line argument and config files; start by locating the argument parser and config-loading entry points. Define how `--type` is represented in configuration and how command-line overrides should behave, then verify required arguments can be omitted from the CLI while existing overrides still work.

Written by the indexing model from the issue text.