memo_template: add new article-class memo template

Replaces the assignment_template with a memo-format template based
on the article class. The look-and-feel is ported from the old
cdsc-memo chapterstyle in cdsc-memoir.sty: a single-line "TITLE
[hfill] AUTHOR" header and sans-serif uppercase section headings.

Like the migrated paper_template, this builds with lualatex and
produces a tagged, PDF/UA-2 compliant PDF. verapdf --flavour ua2:
0 failures, 1723 passed rules.

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

memo_template/.gitignore

@@ -0,0 +1,15 @@
+/auto/
+/cache/
+/vc
+/refs-processed.bib
+/*.aux
+/*.bbl
+/*.blg
+/*.log
+/*.out
+/*.pdf
+/*.fdb_latexmk
+/*.fls
+/*.ttt
+/*.bcf
+/*.run.xml