fix: correct kaniko dockerfile path for docs image build

When --context=docs is set, the --dockerfile path should be relative
to the context directory. Changed from docs/Dockerfile.nginx to
Dockerfile.nginx since kaniko already looks in the docs/ directory.

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

internal/adapter/templates/templates/skeleton/.woodpecker.yml.tmpl

@@ -132,7 +132,7 @@ steps:
           echo "==> No docs/build/ directory, skipping image build"
           exit 0
         fi
-      - /kaniko/executor --dockerfile=docs/Dockerfile.nginx --context=docs --destination=registry.threesix.ai/{{PROJECT_NAME}}-docs:latest --destination=registry.threesix.ai/{{PROJECT_NAME}}-docs:${CI_COMMIT_SHA:0:8}
+      - /kaniko/executor --dockerfile=Dockerfile.nginx --context=docs --destination=registry.threesix.ai/{{PROJECT_NAME}}-docs:latest --destination=registry.threesix.ai/{{PROJECT_NAME}}-docs:${CI_COMMIT_SHA:0:8}
     when:
       branch: main
       event: push