feat: add gemini-cli to x1 system and overlays

- Introduced `gemini-cli` as a CLI tool in the x1 configuration.
- Added a new overlay for `gemini-cli` package with npm dependencies.
- Removed `goose-cli` and `aider-chat` from the existing application list.

systems/x86_64-linux/x1/default.nix

@@ -86,8 +86,7 @@ with lib.metacfg;
     logseq
     claude-code
     claude-desktop-with-fhs
-    goose-cli
-    aider-chat
+    gemini-cli
     vscode
     uv
     #    (vscode-with-extensions.override {