Previously only bitcoind.service showed a version on the tile.
Now every service with a parsable Nix store path gets its version
displayed (electrs, btcpayserver, lnd, rtl, mempool, vaultwarden,
matrix-synapse, caddy, tor, etc.).
The existing _get_service_version() helper reads systemctl show
<unit> --property=ExecStart and extracts the version from the Nix
store path. Results are cached for 5 minutes per unit.
Co-authored-by: arena-agent <297053741+arena-agent@users.noreply.github.com>