feat: bump to NixOS 26.05 (Yarara) — WIP, desktop unverified on hardware

Bumps nixpkgs nixos-25.11 -> nixos-26.05, home-manager release-25.11 ->
release-26.05, and pins stylix to release-26.05 (was unpinned master).
`nix flake check --no-build` and `nomarchy-eval-matrix` are both clean and
the full system builds (nixos-system-nomarchy-26.05).

Breaking-change fixes required by 26.05:
- stylix-compat: drop the `programs.neovim.initLua` shim — HM 26.05 declares
  it natively, so the shim was a duplicate-option error.
- swww was renamed to awww (binaries gone, no `init` subcommand). Dropped swww
  entirely and unified the wallpaper path on swaybg (the daemon this distro
  actually runs): nomarchy-theme-bg-next now delegates to nomarchy-theme-bg-set,
  swaybg added to the theme-engine script deps, swww removed from package lists.
- default config: add a placeholder `fileSystems."/"` — 26.05's systemd stage-1
  forces fsType during plain toplevel eval (the VM build overrides it).
- services.resolved: extraConfig removed, domains/fallbackDns renamed -> migrated
  to settings.Resolve.* (RFC42).
- systemd.sleep.extraConfig removed -> settings.Sleep.HibernateDelaySec (RFC42).
- X11 'virtio' video driver removed -> dropped from vm-guest.nix and
  nomarchy-live.nix (modesetting drives virtio-gpu).
- nomarchy-eval-matrix: define /persist + /home in the impermanence scenarios
  (26.05 maps fsType over every neededForBoot filesystem).
- README/MIGRATION/installer: stale swww references -> swaybg.

KNOWN BLOCKER (why this is on a branch, not main):
In a headless QEMU VM, Hyprland boots and inits GL (virgl) fine but is
OOM-killed after ~19s (3.4 GB peak). Likely a no-display-consumer artifact of
headless rendering (unthrottled frames), but a real Hyprland-26.05 memory
regression can't be ruled out without a real display. Verify on real hardware
(a fresh ISO install) before merging to main; if the desktop is stable there,
the OOM was the headless VM and this can merge.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

bin/utils/nomarchy-eval-matrix

@@ -50,6 +50,16 @@ let
 
   forced = x: (builtins.tryEval (builtins.seq x true)).success;
 
+  # Real impermanence installs define /persist + /home via disko; the eval
+  # scenarios must too, because nixpkgs 26.05's systemd stage-1 maps fsType
+  # over every neededForBoot filesystem and impermanence marks both
+  # neededForBoot (core/system/impermanence.nix). Without device+fsType here,
+  # the toplevel eval throws on a config that has no disko layer.
+  impermanenceFs = {
+    "/persist" = { device = "/dev/disk/by-label/persist"; fsType = "ext4"; };
+    "/home" = { device = "/dev/disk/by-label/home"; fsType = "ext4"; };
+  };
+
   # Combined opt-in scenarios. Each enables as many compatible toggles as
   # possible so CI does ~3 full-system evals, not one per toggle. Home-side
   # options go under home-manager.users.nomarchy.nomarchy.*.
@@ -75,6 +85,7 @@ let
         keymap = { layout = "de"; variant = "nodeadkeys"; };
         toggles = { waybar = false; idle = false; nightlight = false; };
       };
+      fileSystems = impermanenceFs;
     };
 
     # desktop preset — conflicts with the laptop formFactor, so its own eval.
@@ -85,6 +96,7 @@ let
     # impermanence multi-disk variant (alternate mainLuksName).
     "impermanence-multi" = {
       nomarchy.system.impermanence = { enable = true; mainLuksName = "crypted_main"; };
+      fileSystems = impermanenceFs;
     };
   };