Upgrade to Nix 25.11 and migrate configs

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.

ansible/tasks/servers/services/dashy/conf.yml.j2

@@ -30,8 +30,7 @@ sections:
         url: https://drive.mvl.sh
         id: 3_1035_nxtcld
         statusCheck: true
-      - title: ComfyUI
-        icon: http://mennos-server:8188/assets/favicon.ico
+      - title: SD.Next / ComfyUI
         url: http://mennos-server:8188
         statusCheckUrl: http://host.docker.internal:8188/api/system_stats
         id: 3_1035_comfyui