UPDATE: I think I found the answer, see in the Comments section.
Summary: when rendering a table into a block, nothing is displayed. What am I doing wrong?
I've been researching the answer to my question for the past 48 hours, and have held off writing a comment or new forum question so as to not duplicate a question, or ask about something that is clearly documented elsewhere.
I am writing a module to display the results of a very simple query: