Update flake inputs and flake.lock to Nix/nixpkgs and home-manager
release 25.11; bump home.stateVersion and setup script NIXOS_RELEASE.
Migrate git config to new Home Manager layout (programs.git.settings,
aliases under settings.alias), adjust delta config path, and reorganize
SSH into matchBlocks with enableDefaultConfig=false to avoid global
leaks. Simplify snapd session variable handling to avoid recursion.
Misc: tweak Dashy title, replace du-dust->dust and plex-media-player ->
plex-desktop, remove unused hostname arg, and add GitHub Copilot
instructions document.