✨ feat(deploy): Dockerfile + Helm chart for k3s homelab deployment

Pattern adapted from arcodange-org/webapp.

Degraded mode : no DB / no SMTP / no Vault yet, just serves the binary +
swagger + healthz. Subsequent PRs will add Vault auth + Postgres dynamic
credentials + SMTP config.

Ingress route : dancecoachlessons.arcodange.lab (homelab internal).

chart/templates/configmap.yaml

@@ -0,0 +1,9 @@
+apiVersion: v1
+kind: ConfigMap
+metadata:
+  name: {{ include "dance-lessons-coach.fullname" . }}-config
+  namespace: {{ .Release.Namespace }}
+  labels:
+    {{- include "dance-lessons-coach.labels" . | nindent 4 }}
+data:
+{{ toYaml .Values.config | indent 2 }}