review(ahs): match.arg → rlang::arg_match, cli styling, air formatter

[max578]

Lands the code-review polish @adamhsparks authored on review/ahs.
Commits are preserved verbatim under their original authorship; no
history rewriting, no squash.

What this PR contains

Eight commits from @adamhsparks, in order:

• 4d2c7b9 add air formatter support
• cde3f00 format with air
• a12e6d6 format DESCRIPTION and fix Adam's email
• 8f6ace8 replace "i" with i in cli_() calls and use rlang::match_arg(), faster
• d82eee4 lint initial delay, specify integer
• 019963e lint cli messages
• ade53aa ensure user inputs are all upper or lowercase as desired
• c300561 redocument

Known follow-up (to be handled in a second PR)

rlang::arg_match(tolower(backend)) (the single-line form on this
branch) errors under current rlang because arg_match() requires
a symbol, not a call. Fix is a trivial two-line split
(x <- tolower(x); rlang::arg_match(x)) — already prepared on
audit/2026-04-19 which will follow this PR. Does not block merge.

Merge discipline

• Please use "Create a merge commit" or "Rebase and merge" — not
  squash. Squash-merge collapses all 8 commits into one authored by
  whoever clicks the button, which would erase @adamhsparks's
  authorship on main.
• review/ahs should stay on the remote after merge as a contribution
  record. Branch cleanup is @adamhsparks's call.

Test plan

• R CMD check still passes on this branch as-is.
• @adamhsparks approval.

Addresses (partially) #1.

[max578]

Heads-up: once this lands, audit/2026-04-19 follows as a second PR. It
rebases on top of this branch and adds the CRAN-readiness scaffold
(collaboration surface, CITATION.cff / codemeta.json, macos-14 ARM CI
leg, lint + dependency-review workflows, httptest2 REST mocks, cli
snapshot tests), addresses review comments #1 and #3 from #1, adds a
Layer-1 live-GEE integration suite (7 opt-in tests + weekly workflow),
and fixes the two-line form of rlang::arg_match() noted in the PR
description.

Review comment #2 on #1 (yyjsonr over jsonlite) is deferred to a
separate performance PR — documented in audit_2026-04-19.md on the
audit branch so it won't get lost.

Happy to push audit/2026-04-19 to the remote now if you'd like to
review both in parallel, or wait until this merges and push a clean
rebased branch — your call.