Initial commit: CSSS 590 attendance tracker

Publish review_attendance.py, the email and failed-message templates,
and the example config used to track CSSS 590 seminar attendance and
send warning DMs through the Canvas Conversations API. README walks
through the weekly workflow, the Roll Call CSV quirks worth knowing
about, and what must stay out of git.

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

failed_message.txt

@@ -0,0 +1,25 @@
+Greetings {{student}}!
+
+According to my records, you have only taken {{n}} seminars, and not 7 as
+required. Did I miss one? These are the days I have you present/absent
+for:
+
+{{list}}
+
+If my count is incorrect, please let me know which day I'm
+off. Assuming that my count is correct, I can see two ways of handling
+this:
+
+1. I can submit a grade of no credit (NC), which I think is not a huge
+   deal. But maybe you should check with your advisor first?
+
+2. I can submit a grade of I (incomplete) and you can clear it during
+   the second week of the fall quarter by attending the seminar then.
+
+If you go with path 2, you *must* clear the I by the fall quarter
+(which means remembering and reminding me). If you don't, it becomes a
+big, big mess and very likely just turns into NC or a failed grade.
+
+Regards,
+Mako
+