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>

README.md

@@ -8,7 +8,7 @@
 - **Modular Merging Architecture:** Distro code and user code are strictly separated. You can update the distro core without ever touching or breaking your personal configurations.
 - **Interactive "Smart" Installer:** Detects hardware, sets up networking, localizes timezones/keymaps, and offers multi-select software profiles.
 - **Erase Your Darlings (Optional):** Optional BTRFS root-wipe on boot ensures your system stays pristine and 100% declarative.
-- **Dynamic Theming Engine:** 20+ built-in themes with instant UI feedback via IPC (swww, waybar, and stylix).
+- **Dynamic Theming Engine:** 20+ built-in themes with instant UI feedback via IPC (swaybg, waybar, and stylix).
 - **Portable State (`nomarchy-sync`):** Easily backup and sync your declarative config and dynamic state (theme/wallpaper choices) to a private Git repo.
 
 ---