feat: Add zathura config

Note that loading a runtime file in ~/.cache/wal is no longer necessary
since configuration is done declaratively through Nix.

Although this has some downsides, such as the lack of "live reloading"
in some applications, this "feature" wasn't present across all
applications anyway.

modules/desktop.nix

@@ -63,5 +63,15 @@
         mouse.hide_when_typing = true;
       };
     };
+    programs.zathura = {
+      enable = true;
+      options = {
+        guioptions = "v";
+        adjust-open = "width";
+        statusbar-basename = true;
+        render-loading = false;
+        scroll-step = 120;
+      };
+    };
   };
 }