nixos/home-assistant: harden systemd service
nixos/home-assistant: harden systemd service

This is what is still exposed, and it should still allow things to work
as usual.

✗ PrivateNetwork=                    Service has access to the host's …      0.5
✗ RestrictAddressFamilies=~AF_(INET… Service may allocate Internet soc…      0.3
✗ DeviceAllow=                       Service has a device ACL with som…      0.1
✗ IPAddressDeny=                     Service does not define an IP add…      0.2
✗ PrivateDevices=                    Service potentially has access to…      0.2
✗ PrivateUsers=                      Service has access to other users       0.2
✗ SystemCallFilter=~@resources       System call allow list defined fo…      0.2
✗ RootDirectory=/RootImage=          Service runs within the host's ro…      0.1
✗ SupplementaryGroups=               Service runs with supplementary g…      0.1
✗ RestrictAddressFamilies=~AF_UNIX   Service may allocate local sockets      0.1

→ Overall exposure level for home-assistant.service: 1.6 OK :-)

This can grow to as much as ~1.9 if you use one of the bluetooth or nmap
trackers or the emulated_hue component, all of which required elevated
permisssions.

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