fix(regression): separate recipe for bad-restore (custom-html-rst-bad)

Having test_backup.py in custom-html-bkp-bad caused both bad-backup and bad-restore
to fail at the backup tier. Create custom-html-rst-bad with its own cc-ci test dir
that has ops.py+test_restore.py but NO test_backup.py, so:
- backup: only generic test_backup_artifact → PASS (snapshot exists)
- restore: pre_restore writes 'mutated', marker stays 'mutated' after restore → FAIL

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

tests/custom-html-rst-bad/recipe_meta.py

@@ -0,0 +1,3 @@
+# custom-html-rst-bad — regression fixture for bad-restore canary.
+# BACKUP_CAPABLE=True forces the backup tier to run even though the recipe has no backupbot label.
+BACKUP_CAPABLE = True