home/natto: misc changes

enable sioyek
fix gtk theme
add environment variables
change zathura config
change hyprland config

Signed-off-by: Amneesh Singh <natto@weirdnatto.in>

home/natto/programs.nix

@@ -20,6 +20,11 @@
         default-bg = "rgba(0,0,0,0.8)";
       };
     };
+
+    sioyek = {
+      enable = true;
+    };
+
     go.enable = true;
     foot = {
       enable = true;
@@ -59,4 +64,7 @@
       };
     };
   };
+  home.sessionVariables = {
+    BROWSER = "firefox";
+  };
 }