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

The woodpeckerci/plugin-docker-buildx plugin expects build_args as a
YAML map (key: value), not a list. This was causing build args to not
be passed to the Docker build, resulting in unknown git SHA and build
info in the deployed application.

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

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

.woodpecker/.ci.yml

@@ -90,10 +90,10 @@ steps:
       platforms: linux/amd64
       provenance: false
       build_args:
-        - APP_BUILD_VERSION=${CI_COMMIT_SHA:0:8}
+        APP_BUILD_VERSION: ${CI_COMMIT_SHA:0:8}
-        - APP_GIT_SHA=${CI_COMMIT_SHA}
+        APP_GIT_SHA: ${CI_COMMIT_SHA}
-        - APP_BUILD_TIME=${CI_PIPELINE_CREATED}
+        APP_BUILD_TIME: ${CI_PIPELINE_CREATED}
-        - CONTAINER_IMAGE_TAG=${CI_COMMIT_SHA:0:8}
+        CONTAINER_IMAGE_TAG: ${CI_COMMIT_SHA:0:8}
     depends_on: []
     when:
       branch: master