rename: homelab-gateway → telegram-gateway

Aligns the project name with the public URL (tg.arcodange.fr) and the
Arcodange organization conventions. The 'homelab-gateway' name was too
generic.

Touches: chart name + helpers, image registry path, Go module path,
secret/configmap names, deployment mountPath, all docs.

chart/templates/vaultsecret.yaml

@@ -5,7 +5,7 @@ metadata:
   name: bots-secrets
   namespace: {{ .Release.Namespace }}
   labels:
-    {{- include "homelab-gateway.labels" . | nindent 4 }}
+    {{- include "telegram-gateway.labels" . | nindent 4 }}
 spec:
   type: kv-v2
   mount: {{ .Values.vault.mount }}