test(benchmarks): tag tasks as small change, larger implementation, or search

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

scripts/benchmarks/tasks/07-preserve-unknown-settings/task.json

@@ -1,4 +1,5 @@
 {
+  "category": "small change",
   "prompt": "save_settings() loses keys it does not know about when it updates the settings file. Fix it so unknown keys survive.",
   "workflow": {
     "kind": "data-preserving bugfix"