extend (or clarify if already true) uvr import to work for more than just renv

[B-Nilson]

[nbafrank]

Current state: uvr import only handles renv.lock. Other R lockfile / manifest formats worth supporting:

1. DESCRIPTION (R package projects). The parser already exists in crates/uvr-core/src/manifest.rs::parse_description from DESCRIPTION Remotes not handled properly for Suggests or when remote name does not match package name (like for uvr-r and uvr) #68 — it converts Imports/Depends/Suggests/Remotes into uvr.toml. Just needs an uvr import DESCRIPTION autodetect path that routes to that function instead of the renv.lock JSON parser.
2. pak.lock (pak-flavoured lockfile). Similar JSON shape to renv.lock; small adapter.
3. packrat.lock (legacy). Lower priority — packrat is deprecated upstream.

Plan if/when this gets prioritised:

• Detect format by filename (renv.lock / pak.lock / DESCRIPTION / packrat.lock) or --format flag.
• Each format gets a parser → Manifest adapter, all the existing import-merge / project-name / --lock machinery stays.

Not blocking on anything; let me know which formats actually have users and I'll implement them in priority order.