docs(omarchy): #78 Omarchy → Nomarchy migrant one-pager

Add docs/OMARCHY.md for users coming from Omarchy (VISION § F). Leads
with the one real difference — imperative dotfiles vs a declarative flake
built via the menu, with rollback through NixOS generations — then maps
the deltas: install (ISO/nomarchy-install or MIGRATION.md), a familiar
keybindings table, theming (SUPER+T / nomarchy-theme-sync), installing
software (home.packages / nix shell, no AUR), and update+rollback
(nomarchy-pull/-rebuild/-home, boot-menu generations, nomarchy-doctor).
Registered in docs/README.md; VISION § F marked shipped.

The Nomarchy side is grounded in the code: keybindings pulled from
keybinds.nix, and every cited command (7), the nsearch alias, and the
named theme slugs (gruvbox/rose-pine/nord) verified to exist. Omarchy-side
claims kept to known facts (Arch, dotfiles, pacman/AUR).

Verification: V0 (docs-only); commands/slugs/binds checked against the tree.

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

docs/VISION.md

@@ -111,7 +111,7 @@ Reference: [HARDWARE.md](HARDWARE.md) §4–§5, §10.
 
 | Idea | Intent | Notes |
 |------|--------|-------|
-| **Omarchy migrant one-pager** | Bindings/theme/install map | `docs/` short guide |
+| **Omarchy migrant one-pager** ✓ | Bindings/theme/install map | ✓ shipped `docs/OMARCHY.md` (#78, 2026-07-10) |
 | **Hardware hall of fame** | Install-tested models; invite DMI PRs | Ties to HARDWARE.md §9 |
 | **60s demo** | Live → install → theme → menu | Outside repo OK |