rename: braindump → coopertron (Coopertron 5000)

The tool names the whole experiment, not just this script, so it gets a
name with some personality. Repo, directory and command are `coopertron`;
"Coopertron 5000" is the display name in the README and the report title.
The activity the form captures is still a braindump.

Co-Authored-By: Claude Fable 5.1 <noreply@anthropic.com>

tests/fixtures/sample.review.md

@@ -1,4 +1,4 @@
-# Braindump synthesis
+# Coopertron 5000 report
 
 _Generated 2026-10-19 from sample.csv · 12 responses · 71 points · 2 themes · model `tinfoil/glm-5.3`_