Restructure system-modules and bump flake.lock

- Consolidate enable flags into a `packages` attribute in all host
system-modules.nix files. - Rename package option paths to
`config.packages.<name>.enable` in modules/core/packages/packages.nix. -
Update locked revisions (lastModified, narHash, rev) for firefox‑addons
and stylix in flake.lock.

modules/core/packages/packages.nix

@@ -7,9 +7,9 @@
   ...
 }: let
   mkPackage = name: pkgsOrList: {
-    options.${name}.enable = lib.mkEnableOption name;
+    options.packages.${name}.enable = lib.mkEnableOption name;
     config.environment.systemPackages =
-      lib.mkIf config.${name}.enable
+      lib.mkIf config.packages.${name}.enable
       (lib.toList pkgsOrList);
   };