feat(m4): add gemini-cli to default packages

- Included `gemini-cli` to the list of default packages for `aarch64-darwin` platform.
- Ensures availability of the `gemini-cli` tool for users by default.

systems/aarch64-darwin/m4/default.nix

@@ -44,6 +44,7 @@ with lib.metacfg;
     goose-cli
     aider-chat
     fabric-ai
+    gemini-cli
   ];
 
   users.users.harald.shell = pkgs.fish;