feat(gpg): Configure gpg & agent

home/programs/default.nix

@@ -12,6 +12,7 @@
     ./fzf.nix
     ./gh.nix
     ./git.nix
+    ./gpg.nix
     ./hyfetch.nix
     ./just.nix
     ./lazygit.nix

home/programs/gpg.nix

@@ -0,0 +1,17 @@
+{ pkgs, ... }:
+{
+  programs.gpg = {
+    enable = true;
+  };
+
+  services.gpg-agent = rec {
+    enable = true;
+
+    # TODO: Set this to pinentry-curses on non-GUI systems.
+    pinentryPackage = pkgs.pinentry-gtk2;
+
+    # Don't ask for the password very often.
+    defaultCacheTtl = 60480000;
+    maxCacheTtl = defaultCacheTtl;
+  };
+}