feat: initial m3ta-home structure

- flake.nix with nixpkgs, home-manager, nix-colors, m3ta-nixpkgs, agenix, NUR inputs
- lib/mkHome.nix: compose HM config from user + identity + context + sets
- profiles/base: shell, cli-tools, secrets (always loaded)
- profiles/contexts/desktop: WM, apps, theme, ghostty
- profiles/contexts/server: minimal headless
- profiles/sets/coding: core (git, direnv, jq, rg), editor, lsp, languages, agents
- profiles/sets/gaming: steam, gamescope, gpu
- profiles/sets/media: obs, ffmpeg, kdenlive, handbrake, yt-dlp
- users/m3tam3re/identities: private.nix, work.nix (git, jj, ssh per identity)
- users/m3tam3re/preferences: cliphist, difftastic, base packages

profiles/sets/coding/core/git.nix

@@ -0,0 +1,41 @@
+# Git configuration with signing, aliases, and global ignore.
+# Identity and host-specific SSH keys are set per-host in home/m3tam3re/.
+{
+  lib,
+  pkgs,
+  ...
+}:
+with lib; {
+  programs.git = {
+    enable = true;
+    signing.format = null;
+    settings = {
+      user = {
+        name = lib.mkDefault "m3tam3re";
+        email = lib.mkDefault "p@m3ta.dev";
+      };
+      core.excludesfile = "~/.gitignore_global";
+      init.defaultBranch = "master";
+      alias = {
+        st = "status";
+        logd = "log --graph --pretty=format:'%Cred%h%Creset -%C(yellow)%d%Creset %s %Cgreen(%cr) %C(bold blue)<%an>%Creset' --abbrev-commit";
+      };
+    };
+  };
+
+  programs.difftastic.enable = true;
+
+  programs.jujutsu = {
+    enable = true;
+    settings = {
+      user = {
+        email = "m@m3tam3re.com";
+        name = "Sascha Koenig";
+      };
+    };
+  };
+
+  home.packages = with pkgs; [
+    lazygit
+  ];
+}