chore: untrack figaro.test and ignore compiled test binaries

figaro.test is a 13MB compiled ELF test binary, the output of `go test -c`
on the root package. It entered in 3f0405f, a commit about holding the
open region across frames, and no commit has touched it since: it was
carried in by a wide `git add`, not added on purpose.

Ignoring the single filename would only cover the package that happened
to produce this one. Any package can emit a binary named after itself,
so the rule is the extension: `*.test`, which is the line Go's own
gitignore template uses for exactly this. Nothing tracked here ends in
.test, and gitignore does not affect files already tracked, so the
pattern can only catch new ones.

`git rm --cached` only, so the file stays on disk. History is left alone:
purging it from past commits rewrites every hash after 3f0405f, and that
is a separate decision.

Author: gluck

.gitignore

@@ -1,6 +1,10 @@
 /figaro
 /figaro-stripped
 /result
+
+# test binaries, built with `go test -c` or `go test -o`
+*.test
+
 .claude/
 teams.log