fix: update AI Mailer configuration, adjust polling interval, and modify logging level

feat: update NixOS channel to 25.05 and remove unused unstable imports
fix: correct keyboard layout configuration in sway
feat: update ai-mailer package source and hash

hosts/nb/configuration.nix

@@ -4,10 +4,6 @@
 
 { config, lib, pkgs, ... }:
 let
-  unstable = import (fetchTarball https://nixos.org/channels/nixos-unstable/nixexprs.tar.xz) {
-    config = { allowUnfree = true; };
-  };
-
   impermanence = builtins.fetchTarball "https://github.com/nix-community/impermanence/archive/master.tar.gz";
 in {
   nixpkgs.config.allowUnfree = true;