fix(release): rename dockers_v2 to dockers for goreleaser v2 compatibility

goreleaser v2 merged dockers_v2 into dockers; the old key maps to a
deprecated DockerV2 struct that no longer accepts image_templates etc.

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

Author: 2 people

packages/engine/.goreleaser.yaml

@@ -50,7 +50,7 @@ changelog:
     - title: Other
       order: 999
 
-dockers_v2:
+dockers:
   - image_templates:
       - "ghcr.io/dvflw/mantle:{{ .Version }}-amd64"
     use: buildx