add docker backup share

modules/raspi/mount-data.nix

@@ -22,4 +22,26 @@ fileSystems."/mnt/raspi" = {
     "nfsvers=4.2"
   ];
 };
+
+fileSystems."/mnt/raspi-backup" = {
+  device = "raspberrypi.tail13f623.ts.net:/home/raspi/docker-data";
+  fsType = "nfs4";
+  options = [
+    "nofail"
+    "_netdev"
+    "noatime"
+
+    # Don't mount until first access
+    "x-systemd.automount"
+
+    # Unmount after 10 min idle
+    "x-systemd.idle-timeout=600"
+
+    # Give the Pi/Tailscale a little time to appear
+    "x-systemd.device-timeout=10s"
+
+    # Explicitly use NFSv4.2 if supported
+    "nfsvers=4.2"
+  ];
+};
 }