Add home-manager config for sonja from ~/.config/home-manager

Moves home-manager configuration into the flake under home/sonja/,
integrating git, GPG agent, and package config. Fixes deprecated
home-manager options and removes nixpkgs.config override incompatible
with useGlobalPkgs.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

home/sonja/git.nix

@@ -0,0 +1,17 @@
+{ pkgs, ... }:
+
+{
+  programs.git = {
+    enable = true;
+    signing = {
+      key = "0xC3D40E4903C6D427";
+      signByDefault = true;
+    };
+
+    settings = {
+      user.name  = "wytch";
+      user.email = "wytch@sassysalamander.net";
+      gpg.program = "${pkgs.gnupg}/bin/gpg2";
+    };
+  };
+}