feat(fun/uggc): Install desktop handler in Nix derivation

This actually registers the desktop entry, so xdg-open etc. start
working:

tazjin@frog /depot> xdg-open 'uggcf://gjvggre.pbz/alnabgrpu/fgnghf/1272363652679524352'
Opening in existing browser session.

Change-Id: Ia754cb87470fce2f8d3340d1147f3f01b9914858
Reviewed-on: https://cl.tvl.fyi/c/depot/+/387
Reviewed-by: riking <rikingcoding@gmail.com>

fun/uggc/default.nix

@@ -1,14 +1,19 @@
-{ depot, ... }@args:
+{ depot, pkgs, ... }@args:
 
 let
-  gopkgs = depot.third_party.gopkgs;
-in
-depot.nix.buildGo.program {
-  name = "uggc";
-  srcs = [
-    ./main.go
-  ];
-  deps = [
-    gopkgs."github.com".pkg.browser.gopkg
-  ];
-}
+  inherit (pkgs) gopkgs;
+  uggc = depot.nix.buildGo.program {
+    name = "uggc";
+    srcs = [
+      ./main.go
+    ];
+    deps = [
+      gopkgs."github.com".pkg.browser.gopkg
+    ];
+  };
+in uggc.overrideAttrs(old: {
+  buildCommand = old.buildCommand + ''
+    install -D ${./uggc.desktop} $out/share/applications/uggc.desktop
+    sed "s|@out@|$out|g" -i $out/share/applications/uggc.desktop
+  '';
+})

fun/uggc/uggc.desktop

@@ -1,7 +1,7 @@
 [Desktop Entry]
 Type=Application
 Name=Rot13 URL Handler
-Exec=uggc %u
+Exec=@out@/bin/uggc
 StartupNotify=false
 MimeType=x-scheme-handler/uggc;
 MimeType=x-scheme-handler/uggcf;

users/tazjin/nixos/frog/default.nix

@@ -189,9 +189,10 @@ in depot.lib.fix(self: {
   environment.systemPackages =
     # programs from the depot
     (with depot; [
-      fun.idual.script
-      lieer
       frogEmacs
+      fun.idual.script
+      fun.uggc
+      lieer
       ops.kontemplate
       third_party.ffmpeg
       third_party.git