Update to (somewhat?) dendritic pattern

Heavily inspired by https://github.com/Doc-Steve/dendritic-design-with-flake-parts.

> Atomic commits? Never heard of them!

modules/programs/zsh/zsh.nix

@@ -0,0 +1,53 @@
+{ inputs, ... }: {
+  flake.modules.nixos.zsh = {
+    programs.zsh.enable = true;
+
+    environment.pathsToLink = [ "/share/zsh" ];
+  };
+
+  flake.modules.homeManager.zsh = { pkgs, ... }: {
+    imports = with inputs.self.modules.homeManager; [
+      fzf
+      zoxide
+    ];
+
+    programs.zsh = {
+      enable = true;
+
+      autocd = true;
+      enableCompletion = true;
+      autosuggestion.enable = true;
+      syntaxHighlighting.enable = true;
+      initContent = pkgs.lib.mkBefore ''
+        date
+        # Enable Powerlevel10k instant prompt. Should stay close to the top of ~/.zshrc.
+        # Initialization code that may require console input (password prompts, [y/n]
+        # confirmations, etc.) must go above this block; everything else may go below.
+        if [[ -r "''${XDG_CACHE_HOME:-$HOME/.cache}/p10k-instant-prompt-''${(%):-%n}.zsh" ]]; then
+          source "''${XDG_CACHE_HOME:-$HOME/.cache}/p10k-instant-prompt-''${(%):-%n}.zsh"
+        fi
+      '';
+
+      plugins = [
+        {
+          name = "powerlevel10k";
+          src = "${pkgs.zsh-powerlevel10k}/share/zsh-powerlevel10k/";
+          file = "powerlevel10k.zsh-theme";
+        }
+        {
+          name = "p10k-config";
+          src = ./p10k;
+          file = "p10k.zsh";
+        }
+      ];
+
+      oh-my-zsh = {
+        enable = true;
+        plugins = [
+          "git"
+        ];
+        theme = "robbyrussell";
+      };
+    };
+  };
+}