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/refs.bib

@@ -0,0 +1,14 @@
+@inproceedings{989866,
+  author =	 {Ken Hinckley and Gonzalo Ramos and François
+                  Guimbretiere and Patrick Baudisch and Marc Smith},
+  title =	 {Stitching: pen gestures that span multiple displays},
+  booktitle =	 {AVI '04: Proceedings of the working conference on
+                  Advanced visual interfaces},
+  year =	 {2004},
+  isbn =	 {1-58113-867-9},
+  pages =	 {23--31},
+  location =	 {Gallipoli, Italy},
+  doi =		 {http://doi.acm.org/10.1145/989863.989866},
+  publisher =	 {ACM Press},
+  address =	 {New York, NY, USA},
+}