nixpkgs: Refresh channels and inputs

Rebase the fork branches and refresh nixpkgs, home-manager, and the
approved ancillary inputs. Update kernel and release metadata, adapt
removed package and Home Assistant options, and keep Determinate Nix
on its tested nixpkgs revision to avoid duplicate Boost patches.

Retire Sharry and its public endpoint because copyparty replaces it.
Document the GitHub mirror gate and require real devshell and system
builds in the upgrade validation workflow.

nixos/default.nix

@@ -191,7 +191,7 @@ let
       # Routes the custom modules into `baseModules` so the NixOS manual documents them. The old
       # infinite-recursion is gone, but enabling this makes every system build regenerate the
       # manual, and it documents everything the modules transitively import — including third-party
-      # modules that aren't doc-clean (e.g. `services.sharry`). Prefer the generated
+      # modules that aren't doc-clean. Prefer the generated
       # `nixos.optionsDoc` reference (`docs/reference/nixos-options.md`) instead.
       docCustom = mkBoolOpt' false "Whether to document nixfiles' custom NixOS modules.";