fix(restic): use the correct systemd timer option names (#319)

timerConfig was set with lowercase onCalendar/randomizedDelaySec, which systemd treats as unknown directives. The generated timer had no schedule, so `systemctl list-timers` showed NEXT=- and no backup ever ran. Use the real keys OnCalendar/RandomizedDelaySec.

modules/nixos/base/restic-backup.nix

@@ -163,7 +163,8 @@ in
       ++ cfg.exclude;
 
       timerConfig = {
-        inherit (cfg) onCalendar randomizedDelaySec;
+        OnCalendar = cfg.onCalendar;
+        RandomizedDelaySec = cfg.randomizedDelaySec;
       };
 
       inherit (cfg) pruneOpts;