feat(ai): add webdav mount (#253)

feat(aquamarine): add group for filesharing, protect /data on subvolume mount failures

modules/nixos/base/user-group.nix

@@ -19,6 +19,9 @@
     plugdev = { };
     # misc
     uinput = { };
+    # shared group for services that read/write the same data directory
+    # (e.g. sftpgo + transmission on aquamarine)
+    fileshare = { };
   };
 
   users.users."${myvars.username}" = {
@@ -36,6 +39,7 @@
       "wireshark"
       "adbusers" # android debugging
       "libvirtd" # virt-viewer / qemu
+      "fileshare"
     ];
   };