feat: migrate command scripts to just

- Replaced bin/ shell scripts with a Justfile
- Added deploy commands and 2 new commands (update, gc)
- Added just to devShell

justfile

@@ -0,0 +1,21 @@
+#!/usr/bin/env -S just --justfile
+
+default:
+  @just --list
+
+deploy-nixos:
+  sudo nixos-rebuild switch --flake .#$(hostname)
+
+deploy-vps:
+  nixos-rebuild switch --flake .#vps --target-host root@vps
+
+deploy-home:
+  home-manager switch --flake .#$USER@$(hostname)
+
+update:
+  nix flake update --commit-lock-file
+
+gc:
+  nix-collect-garbage -d
+  nix-collect-garbage --delete-older-than 7d
+  nix-store --gc