Fix policy form roles; add JSON edit mode

- Replace stale "service" role option with correct set:
  admin, user, guest, viewer, editor, commenter (matches model.go)
- Add Form/JSON tab toggle to policy create form
- JSON tab accepts raw RuleBody JSON with description/priority
- Handler detects rule_json field and parses/validates it
  directly, falling back to field-by-field form mode otherwise

.junie/memory/language.json

@@ -1 +1 @@
-[{"lang":"en","usageCount":3}]
+[{"lang":"en","usageCount":7}]