ci: trust artifactapi internal CA when pushing docker-internal

The v0.1.0 release pipeline built the runtime image fine but failed the
push to artifactapi.k8s.syd1.au.unkin.net/docker-internal with a TLS
x509 unknown-authority error: buildkit did not trust artifactapi's
Vault-signed cert.

Stage the internal CA into the shared workspace via the almalinux9-base
image (already trusts the unkin CA; same image the RPM release pipelines
use to reach artifactapi over HTTPS) and point the docker-buildx plugin
at it through buildkit_config. buildx copies the referenced CA into the
buildkitd container at builder-create time, so the push handshake now
verifies. No credentials needed: anonymous push to docker-internal is
allowed for trusted clients.

.woodpecker/docker.yaml

@@ -24,17 +24,44 @@ steps:
             memory: 6Gi
             cpu: 4
 
+  # Stage the internal (Vault) CA into the shared workspace so the buildkit push
+  # below can verify artifactapi's TLS cert. almalinux9-base already trusts the
+  # unkin CA (it is the image the RPM release pipelines use to reach artifactapi
+  # over HTTPS), so its consolidated trust bundle contains the chain we need.
+  - name: ca-trust
+    image: git.unkin.net/unkin/almalinux9-base:20260606
+    commands:
+      - cp /etc/pki/tls/certs/ca-bundle.crt "$${CI_WORKSPACE}/artifactapi-ca.crt"
+    depends_on: [publish]
+    backend_options:
+      kubernetes:
+        serviceAccountName: default
+        resources:
+          requests:
+            memory: 256Mi
+            cpu: 250m
+          limits:
+            memory: 512Mi
+            cpu: 1
+
   # Build the runtime image and push it to the artifactapi local docker registry.
+  # buildkit_config points buildkit at the staged CA so the TLS handshake with
+  # artifactapi (Vault-signed cert) verifies; buildx copies the referenced CA
+  # into the buildkitd container under /etc/buildkit/certs when it creates the
+  # builder. CI_WORKSPACE is runtime-only so the path is the fixed workspace path.
   - name: docker
     image: woodpeckerci/plugin-docker-buildx
     settings:
       registry: artifactapi.k8s.syd1.au.unkin.net
       repo: artifactapi.k8s.syd1.au.unkin.net/docker-internal/jellyfin-ha
       dockerfile: Dockerfile.runtime
+      buildkit_config: |
+        [registry."artifactapi.k8s.syd1.au.unkin.net"]
+          ca = ["/woodpecker/src/git.unkin.net/unkin/jellyfin-ha/artifactapi-ca.crt"]
       tags:
         - ${CI_COMMIT_TAG}
         - latest
-    depends_on: [publish]
+    depends_on: [ca-trust]
     backend_options:
       kubernetes:
         serviceAccountName: default