ci: push images to artifactapi registry instead of gitea

Hard switch of the docker push target from the Gitea registry to the
artifactapi local docker registry (docker-internal); the Gitea VM and its
registry are being retired. Drops the droneci/DRONECI_PASSWORD creds since
artifactapi accepts unauthenticated in-cluster pushes.

Claude-Session: https://claude.ai/code/session_015ur3i7D2azsMAWTSVABApv

.woodpecker/build.yaml

@@ -5,5 +5,5 @@ steps:
   - name: docker-build
     image: woodpeckerci/plugin-docker-buildx
     settings:
-      repo: git.unkin.net/unkin/age-api
+      repo: artifactapi.k8s.syd1.au.unkin.net/docker-internal/age-api
       dry_run: true

.woodpecker/docker.yaml

@@ -6,11 +6,8 @@ steps:
   - name: docker
     image: woodpeckerci/plugin-docker-buildx
     settings:
-      registry: git.unkin.net
-      repo: git.unkin.net/unkin/age-api
-      username: droneci
-      password:
-        from_secret: DRONECI_PASSWORD
+      registry: artifactapi.k8s.syd1.au.unkin.net
+      repo: artifactapi.k8s.syd1.au.unkin.net/docker-internal/age-api
       tags:
         - ${CI_COMMIT_TAG}
         - latest