Replace gt dependency with lt

[yihui]

Summary

• Remove the gt package from Imports and replace with the lightweight lt package
• New as_lt() generic + S3 methods for fixed_design_summary and gs_design_summary, fully replacing as_gt()
• All 14 vignettes updated to use lt functions (lt(), lt_header(), lt_spanner(), lt_format(), lt_footnote(), lt_note(), lt_cols_label())
• README.Rmd updated to use knitr::kable() for GitHub rendering and show lt API in code examples
• Tests updated for lt_tbl assertions

New lt features required (committed in yihui/lt)

• lt_cols_label(): rename column display headers without modifying data frame columns
• lt_footnote(match = "starts_with"): target all row groups whose label starts with a prefix (used for "Analysis: ..." groups)

Migration mapping

gt	lt
gt::gt(x)	lt(x)
group_by(col) |> gt()	lt(x, row_group = "col")
tab_header(title, subtitle)	lt_header(title, subtitle)
tab_spanner(label, columns)	lt_spanner(label, columns)
fmt_number(columns, decimals)	lt_format(columns, decimals)
tab_footnote(fn, cells_column_labels(col))	lt_footnote(text, "column", columns)
tab_footnote(fn) (no location)	lt_note(text)
cols_label(a = "A")	lt_cols_label(a = "A")

Test plan

• as_lt() unit tests pass for fixed and GS designs
• All design types render correctly (fixed_ahr, gs_ahr, gs_wlr, gs_rd)
• Visual comparison with gt output confirms structural equivalence
• Non-binding design body footnote renders correctly
• Custom footnotes (colname, title, analysis, spanner) all work
• R CMD check passes
• All vignettes build without error

🤖 Generated with Claude Code

[jdblischak]

When I run the tests locally, I get two failures:

library("testit")
test_pkg()
## Error: -- Assertion failed: as_lt: footnote=FALSE removes footnote --
##    1. count_footnotes(z1) (LHS) ==>
##        int 0
##       ----------
##        int 1
##       <== (RHS) 1L
##       count_footnotes(z1) %==% 1L is not TRUE but FALSE at tests/testit/test-developer-as_lt.R#14
##    2. count_footnotes(z1) (LHS) ==>
##        int 0
##       ----------
##        int 2
##       <== (RHS) 2L
##       count_footnotes(z1) %==% 2L is not TRUE but FALSE at tests/testit/test-developer-as_lt.R#22

sessioninfo::package_info(c("gsDesign2", "lt"), dependencies = FALSE)
##  package   * version date (UTC) lib source
##  gsDesign2 * 1.1.8   2026-05-28 [1] local
##  lt          0.0.7   2026-05-28 [1] Github (yihui/lt@e485eb6)
##
##  [1] C:/Users/john/AppData/Local/R/win-library/4.4
##  [2] C:/Program Files/R/R-4.4.3/library
##  * ── Packages attached to the search path.

[jdblischak]

Since as_gt() is an exported function, should we have at least one release where it is marked as deprecated before we actually remove it?

#' @export
as_gt <- function(x, ...) {
  .Deprecated("as_lt")
  UseMethod("as_gt", x)
}

[jdblischak]

And for a visual comparison, below is what I see in the RStudio Viewer on Windows for the last table produced by example("as_gt") or example("as_lt")

as_gt()

as_lt()

[yihui]

@jdblischak Thanks for the feedback! This PR is still a draft, and all issues will be addressed. The final goal is to eliminate most (if not all) visual differences. I'll ping you and Yujie when the PR is ready for review.