lib/regex: rehome private-touching @tests to in-package regex_whitebox.ww

White-box @tests move into a colocated 'package regex' file (Hare
+test.ha analogue; #6 non-T drop plays the build-tag role), black-box
@tests stay in package regex_test — Go's foo/foo_test split. The
wb/ stub driver is documented-temporary scaffolding: a same-dir
importer file-resolves to regex.ww before dir-enumeration, so only a
different-dir import bundles the whitebox sibling (task #33 retires
it). CLAUDE.md rule-9 carve-out updated (#5 closed, gate was #6).

test/wcc/989_lib_byteid.c

@@ -85,6 +85,10 @@ static const struct ent ents[] = {
 	{ .fixture = "lib/memio/memiotest.ww",             .mode = M_ID },
 	{ .fixture = "lib/os/ostest.ww",                   .mode = M_ID },
 	{ .fixture = "lib/regex/regex_test.ww",            .mode = M_ID },
+	/* in-package white-box half (#9): the wb/ driver dir-resolves
+	 * `import regex` and bundles lib/regex/regex_whitebox.ww (package
+	 * regex), so this fixture byte-ids the moved engine probes. */
+	{ .fixture = "lib/regex/wb/regex_test.ww",         .mode = M_ID },
 	{ .fixture = "lib/strconv/test/ftostest.ww",       .mode = M_ID },
 	/* graduated from #59.10 DIVERGE by the #62 float-literal fold fix
 	 * (wwstage lexer now folds through strconv.stof64, matching