Switch to lualatex and generate accessible PDF/UA-2 output

Add \DocumentMetadata for PDF 2.0 / PDF/UA-2, load tagpdf with
activate-all, extend hypersetup with pdftitle/pdfauthor/pdflang/
pdfdisplaydoctitle, and add alt text to the letterhead and signature
images. Drop xetex-only xltxtra and switch the Makefile from xelatex
to lualatex. Verified compliant with verapdf's PDF/UA-2 profile.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

Makefile

@@ -11,7 +11,7 @@ figures/signature.pdf:
 	gpg --yes --output $(DEC_SIGIMAGE) --decrypt $(ENC_SIGIMAGE)
 
 %.pdf: %.tex
-	latexmk -f -xelatex $<
+	latexmk -f -lualatex $<
 
 clean:
 	latexmk -C *.tex

washington_letterhead_letter-matrix-deptartment.tex

@@ -1,3 +1,8 @@
+\DocumentMetadata{
+  pdfversion=2.0,
+  pdfstandard=ua-2,
+  lang=en-US,
+}
 \documentclass[11pt,letterpaper]{article}
 
 % MODIFY THE DETAILS IN THIS SECTION TO MATCH WHAT YOU WANT ON /YOUR/ LETTERHEAD
@@ -6,12 +11,16 @@
 \def\phone{mobile 206-409-7191}
 \def\email{makohill@uw.edu}
 \def\web{https://mako.cc/academic/}
+\def\lettertitle{Letter from \email}
+\def\letterauthor{John Hancock}
 
 \usepackage[top=1.25in,left=1.25in,bottom=1.20in,right=1.25in]{geometry}
 
-\usepackage{xltxtra}
-
 \usepackage{fontspec}
+\usepackage{tagpdf}
+\tagpdfsetup{activate-all}
+\newopentypefeature{Contextuals}{NoAlternate}{-calt}
+\defaultfontfeatures{Kerning=Uppercase,Ligatures=TeX}
 
 \setsansfont{OpenSans}[
 Path = ./fonts/OpenSans/,
@@ -31,6 +40,11 @@ BoldItalicFont  =   *-BoldItalic
 \usepackage[colorlinks=false,
             pdfborder={0 0 0},
             ]{hyperref}
+\hypersetup{unicode=true,
+    pdftitle={\lettertitle},
+    pdfauthor={\letterauthor},
+    pdflang={en-US},
+    pdfdisplaydoctitle=true}
 \usepackage{tikz}
 
 \usepackage{lastpage}
@@ -43,7 +57,7 @@ BoldItalicFont  =   *-BoldItalic
   \ifnum\thepage=1
   \begin{tikzpicture}[remember picture,overlay,every node/.style={inner sep=0,outer sep=0}]
     \node at (current page.north west) [anchor=north west]
-    {\includegraphics{figures/matrix_header.pdf}};
+    {\includegraphics[alt={University of Washington letterhead}]{figures/matrix_header.pdf}};
     % add the department name
     \node at (current page.north west) [anchor=north west, xshift=1.19in, yshift=-0.56in]
     {{\fontsize{14pt}{16pt} \fontspec{MatrixIIOT-Book.otf}[
@@ -127,7 +141,7 @@ Sed ullamcorper morbi tincidunt ornare massa eget egestas purus. Feugiat pretium
 
 Sincerely,
 
-\includegraphics[width=1.7in]{figures/signature.pdf}\\
+\includegraphics[width=1.7in,alt={Signature of \letterauthor}]{figures/signature.pdf}\\
 John Hancock\\
 Assistant Professor of Communication\\
 Adjunct Assistant Professor of Human-Centered Design and Engineering