Problem: Forge metadata fetching required manual token management —
config fields, CLI token extraction, and curl with auth headers. Each
forge had a different auth path, and Codeberg had no CLI support at all.
Solution: Delete `get_token()` and `_api_url()`, replace with
`_api_args()` that builds `gh api`, `glab api`, or `tea api` arg
arrays. The CLIs handle auth internally. Add `warn_missing_cli` config
(default true) that warns once per forge per session on failure. Add
forge CLI checks to `:checkhealth`. Remove `token` from config/docs.