fix(ci): Use YAML list format for docker-buildx build_args

The woodpecker docker-buildx plugin requires build_args as a YAML list,
not a comma-separated string. This fixes the build version/hash not being
passed to the Docker image.

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

.woodpecker/.ci.yml

@@ -64,7 +64,11 @@ steps:
         from_secret: registry_password
       platforms: linux/amd64
       provenance: false
-      build_args: APP_BUILD_VERSION=${CI_COMMIT_SHA},APP_GIT_SHA=${CI_COMMIT_SHA},APP_BUILD_TIME=${CI_PIPELINE_CREATED},CONTAINER_IMAGE_TAG=${CI_COMMIT_SHA}
+      build_args:
+        - APP_BUILD_VERSION=${CI_COMMIT_SHA}
+        - APP_GIT_SHA=${CI_COMMIT_SHA}
+        - APP_BUILD_TIME=${CI_PIPELINE_CREATED}
+        - CONTAINER_IMAGE_TAG=${CI_COMMIT_SHA:0:8}
     depends_on: []
     when:
       branch: master