Add host printer configs and refactor printing

Add printers.nix for Garand‑Desktop, Garand‑Laptop, and default hosts
with
printer definitions and a printEnable flag. Disable NFS by default in
the
host variables. Rewrite modules/core/printing.nix to import printer
settings, enable services only when printing is enabled, and add more
CUPS/Avahi options plus hardware.printers configuration. Add the lpadmin
group to the main user. Update the Messenger desktop entry URL to the
Facebook Messages page.

hosts/Garand-Laptop/printers.nix

@@ -0,0 +1,14 @@
+{
+  printEnable = true;
+
+  ensureDefaultPrinter = "Brother-T525W";
+
+  ensurePrinters = [
+    {
+      deviceUri = "ipp://192.168.1.110/ipp";
+      location = "home";
+      name = "Brother-T525W";
+      model = "everywhere";
+    }
+  ];
+}

hosts/Garand-Laptop/variables.nix

@@ -33,10 +33,7 @@
   nvidiaID = "PCI:0:2:0";
 
   # Enable NFS
-  enableNFS = true;
-
-  # Enable Printing Support
-  printEnable = false;
+  enableNFS = false;
 
   # Set Stylix Image
   # This will set your color palette