Add railiance01 deployment artifacts and fix container image build

Introduce Dockerfile, entrypoint, and k8s/railiance manifests for the
ArgoCD GitOps pilot (ISSUE-WP-0003). Rename the Gitea PyPI build arg to
GITEA_PYPI_INDEX_URL so pip still resolves dependencies from PyPI.

k8s/railiance/kustomization.yaml

@@ -0,0 +1,12 @@
+# issue-core workload manifests, synced by the ArgoCD `issue-core` Application
+# (path k8s/railiance, destination namespace issue-core, CreateNamespace=true).
+apiVersion: kustomize.config.k8s.io/v1beta1
+kind: Kustomization
+
+namespace: issue-core
+
+resources:
+  - externalsecret.yaml
+  - configmap-backends.yaml
+  - deployment.yaml
+  - service.yaml