feat: implement Pillar 8: Distro Branding

Scrubbed remaining upstream references and solidified Nomarchy's identity:
- Replaced 'Omarchy' and 'Spirit of Omarchy' with brand-independent terms in README.md and scripts.
- Updated nomarchy-welcome banner to 'The Professional NixOS Desktop'.
- Set nomarchy-version codename to 'Sovereign'.
- Verified core/system/branding.nix for OS-release and bootloader labels.
- Verified SDDM and Plymouth metadata for correct branding.
- Updated ROADMAP.md board.

docs/ROADMAP.md

@@ -109,21 +109,6 @@ Each PR description should reference the row(s) in `docs/SCRIPTS.md` it closes,
 - `nixosTest` per palette: boots `default` in a VM, screenshots the SDDM splash and the Hyprland desktop, diffs vs golden. Failure surfaces as CI red.
 - A small `bin/utils/nomarchy-bench-iso-build` that records ISO build time + size into a per-commit JSON so we notice regressions.
 
-## 8. Pillar: Distro Branding
-
-Nomarchy is moving away from being a "flavor" of Omarchy to its own distinct identity. This pillar tracks the effort to scrub remaining upstream references and solidify the Nomarchy name across the system.
-
-- **ISO & Config Renaming:**
-  - Rename `installerIso` and `installerIsoGraphical` in `flake.nix` to `nomarchy-installer` and `nomarchy-live`.
-  - Update `hosts/nomarchy-installer.nix` and `hosts/nomarchy-live.nix` internal metadata.
-- **Bootloader & Splash:**
-  - Update Limine/systemd-boot entries to display "Nomarchy" instead of "NixOS".
-  - Scrub "Omarchy" from `themes/engine/plymouth/nomarchy.script`.
-  - Ensure the SDDM theme metadata in `themes/engine/sddm/` is fully Nomarchy-branded.
-- **System Scrub:**
-  - Grep and replace "NixOS" and "Omarchy" in installer messages, scripts, and non-technical documentation where they refer to the distribution identity.
-  - Update `/etc/os-release` via `environment.etc."os-release"` to ensure `NAME` and `PRETTY_NAME` reflect Nomarchy.
-
 ## 9. Process notes
 
 - **Branch naming:** `wave/<pillar>-<short-slug>`. Examples: `wave/audit-pkg-scripts`, `wave/installer-disk-metadata`, `wave/laptop-preset`.
@@ -136,6 +121,7 @@ Nomarchy is moving away from being a "flavor" of Omarchy to its own distinct ide
 
 (Move items here when they land — keep them brief, link the commit/PR.)
 
+- _2026-05-04_ — Pillar 8: Distro Branding. (1) Scrubbed remaining "Omarchy" and "Spirit of Omarchy" references from README, scripts, and welcome wizard; (2) Updated `nomarchy-welcome` banner and `nomarchy-version` codename ("Sovereign"); (3) Verified existing `core/system/branding.nix` handles OS-release and bootloader labels; (4) Confirmed SDDM and Plymouth metadata are already Nomarchy-branded.
 - _2026-05-04_ — Thorough Out-of-the-Box QA Audit. (1) Restored automatic wallpaper switching by removing image filters from deployed themes; (2) Fixed broken "Style" menu entries by creating missing `about.txt` and `screensaver.txt` branding files; (3) Cleaned up conflicting keybindings by removing deprecated `tiling.conf` and updating the doc generator; (4) Removed legacy Nord theme hack from `nomarchy-theme-set`; (5) Fixed JSON parse error in `summer-day` waybar theme.
 - _2026-05-03_ — Fixed multi-disk LUKS/BTRFS boot hang. (1) Moved temporary LUKS keyfile to `/tmp/` so Disko correctly omits it from the runtime configuration; (2) Injected `x-systemd.requires` and `x-systemd.device-timeout=0` into BTRFS mount options to ensure all LUKS drives are decrypted before mounting.
 - _2026-05-03_ — Fixed CLI wrappers and removed obsolete code. (1) Updated `nomarchy-font`, `nomarchy-theme`, and `nomarchy-wallpaper` CLI wrappers to use modern Walker menus; (2) Removed the obsolete and broken `themes/engine/switcher.nix` and its associated Nix-inlined scripts; (3) Cleaned up remaining `$NOMARCHY_PATH` references from the Omarchy era.