✨ 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/serviceaccount.yaml

@@ -0,0 +1,13 @@
+{{- if .Values.serviceAccount.create -}}
+apiVersion: v1
+kind: ServiceAccount
+metadata:
+  name: {{ include "dance-lessons-coach.serviceAccountName" . }}
+  labels:
+    {{- include "dance-lessons-coach.labels" . | nindent 4 }}
+  {{- with .Values.serviceAccount.annotations }}
+  annotations:
+    {{- toYaml . | nindent 4 }}
+  {{- end }}
+automountServiceAccountToken: {{ .Values.serviceAccount.automount }}
+{{- end }}