Reorganize loose modules into themed directories

Several single-purpose modules sat at modules/ root or in the
services/ catch-all despite the repo's established pattern of one
directory per concern (tailscale/, beszel/, docker/, nix-cache/):

- remote-builder-client.nix -> nix-cache/ (always co-included with
  nix-cache/client.nix in flake.nix's mkTarget, same buildType guard)
- set-locale.nix -> common/ (unconditionally imported by
  common/configuration.nix already)
- enable-ip-forwarding.nix -> networking/
- rotate-traefik-logs.nix -> traefik/rotate-logs.nix
- services/docker-health-to-gotify.nix and services/nextcloud-cron-job.nix
  -> docker/ (both only ever imported by the docker build type, same
  as the rest of modules/docker/*)

Pure path moves plus import-path updates in flake.nix,
common/configuration.nix, and build-types/docker.nix — verified
eval-equivalent (drvPath-identical) across representative hosts.

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01La55Nsss8jZ7ZuzUV9mfot

modules/docker/docker-health-to-gotify.nix

@@ -0,0 +1,28 @@
+{ pkgs, vars, ... }:
+
+{
+  systemd.services.docker-health-to-gotify = {
+    description = "Alert Gotify when Docker containers become unhealthy";
+    after = [ "docker.service" ];
+    serviceConfig = {
+      Type = "oneshot";
+      # Run as root so it can read /etc/secrets and access docker socket
+      # User = "root";
+      #EnvironmentFile = "-/etc/secrets/docker-health-alert.env";
+      ExecStart = "${pkgs.bash}/bin/bash /home/${vars.primaryUser}/docker/monitoring/gotify/docker-health-to-gotify.sh";
+      StandardOutput = "journal";
+      StandardError = "journal";
+    };
+    path = with pkgs; [ docker curl coreutils gnused ];
+  };
+
+  systemd.timers.docker-health-to-gotify = {
+    wantedBy = [ "timers.target" ];
+    timerConfig = {
+      OnBootSec = "2min";
+      OnUnitActiveSec = "1min";
+      AccuracySec = "15s";
+      Persistent = true;
+    };
+  };
+}

modules/docker/nextcloud-cron-job.nix

@@ -0,0 +1,22 @@
+{ pkgs, vars, ... }:
+
+{
+  # Create nextcloud cron scheduled task
+  systemd.services.nextcloud = {
+    description = "Nextcloud scheduled task";
+    script = ''${pkgs.bash}/bin/bash ~/docker/services-up.sh --profile nextcloud exec -u 33 nextcloud-webapp php ./cron.php'';
+    serviceConfig = {
+      Type = "oneshot";
+      User = vars.primaryUser;
+    };
+    path = with pkgs; [ docker docker-compose ];
+  };
+
+  systemd.timers.nextcloud = {
+    wantedBy = [ "timers.target" ];
+    timerConfig = {
+      OnCalendar = "*:0/5";
+      Persistent = true;
+    };
+  };
+}