Fix goreleaser deprecation warnings

- archives.format → archives.formats (now a list)
- archives.builds → archives.ids (renamed for consistency)
- dockers → dockers_v2 (new consolidated docker config)
- Update Dockerfile to use TARGETPLATFORM build arg

https://claude.ai/code/session_01QqkHTjwoFvsNUXtQj3RaU8

Dockerfile

@@ -1,5 +1,6 @@
 FROM scratch
 ENV PATH "$PATH:/bin"
-COPY tomll /bin/tomll
-COPY tomljson /bin/tomljson
-COPY jsontoml /bin/jsontoml
+ARG TARGETPLATFORM
+COPY $TARGETPLATFORM/tomll /bin/tomll
+COPY $TARGETPLATFORM/tomljson /bin/tomljson
+COPY $TARGETPLATFORM/jsontoml /bin/jsontoml