Quarto support

[gaborcsardi]

Now that we have good tools for virtual environments, inline scripts and script lock files, we could easily add support for building quarto documents inside projects, including requirements in stand-alone quarto documents and creating lock files for qmds.

Possible API:

rig quarto render   [rig options] [<doc>] [quarto args...]
rig quarto preview [rig options] [<doc>] [quarto args...]

• rig options go before the doc: --r-version, --no-project, --upgrade, --upgrade-package, --locked, --dry-run. Everything after the doc goes to quarto.
• Inside a project we run the document in the project environment. --no-project opts out. A rig: formatter key in a document inside a project could be an error, maybe?
• Outside a project, use the rig: key in the YAML front matter, with the same tables as the script block in inline scripts.
• If there is no rig: block, use the default R version or --r-version.
• Should we warn if rmarkdown is not installed and the document needs it?
• Should we have rig quarto install to install quarto?

Example front matter for standalone files:

---
title: Report
rig:
  dependencies:
    R: ">= 4.4"
    dplyr: ">= 1.1"
  repository: [...]        # optional
  tool:
    rig:
      exclude-newer: "2026-06-01"
---

Locking individual documents works the same way as scripts:

rig proj init --script report.qmd          # create qmd file with rig header
rig proj lock --script report.qmd          # lock qmd file, create report.qmd.lock
rig proj add --script report.qmd           # add dependency to report
rig proj remove --script report.qmd        # remove dependency from report