fix: .custard.yaml source: tag (custard release pushes a tag; bookmark mode skipped the publish)

@@ -5,6 +5,5 @@   - go vet ./...
   - go test ./...
 brew:
   enabled: true
-  package: "."            # main is at the repo root
-  source: bookmark        # jj-native: release ref = release/vX.Y.Z bookmark
-  bookmark_prefix: "release/"
+  package: "."     # main is at the repo root
+  source: tag      # `custard release vX.Y.Z` tags + pushes; the forge publishes from the tag