feat(themes): wallpapers split — 94 MB of runtime-only images leave the flake source

The split line is consumption time: palette JSONs, previews and
per-theme overrides are read at Nix eval and stay in-repo (~3 MB);
wallpapers are runtime-only (swww via nomarchy-state-sync, never read
at eval) and move to the pinned nomarchy-wallpapers non-flake input
(git.bemagri.xyz/bernardo/Nomarchy-Wallpapers @ 803b48d, all 24 slugs).

New overlay drv nomarchy-default-themes merges the two: repo themes
copied, <slug>/backgrounds symlinked from the input, build FAILS if any
theme JSON lacks non-empty backgrounds — the drift guard for the
two-repo dance. nomarchy-state-sync's wrapper now points straight at
the merged store path (no in-package copy): the package drops from
~94 MB to 32.6 KiB and the wallpapers source appears exactly once in
any system closure, ISO included — offline promise intact. Downstream
custom wallpapers still win ($NOMARCHY_PATH/themes is checked first),
and an explicit state.json wallpaper path still works.

checks re-pointed at the merged tree (theme-wholeswap,
state-sync-validate, auto-theme); theme-contrast and airplane stay on
./themes (JSON/text only). import-palettes.py + README updated;
ROADMAP § Faster switches marked shipped; LATER now carries only the
pre-built-variants follow-on. Also files #151 (v1 launch plan, [human])
with measured history numbers: the 107 MiB pack is 94 MB wallpaper
blobs; all 848 text commits pack to ~15-20 MiB — recommendation
recorded to filter-repo at the GitHub move, not fresh-start.

Verification: V2 — nix flake check --no-build green; theme-wholeswap,
state-sync-validate, auto-theme VM check, downstream-template-home all
green; wallpapers store path exactly once in the state-sync closure;
`list` works from a scratch state dir. V3 queued: live wallpaper render
+ bg-next + custom-override precedence after next pull (HARDWARE-QUEUE).
Lock gained exactly the one input node. Implementation by a Sonnet
subagent; design and review on Fable.

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

docs/ROADMAP.md

@@ -193,7 +193,7 @@ Design/decision records and a running log of shipped work (items marked
   rendered + captured); real-hardware capture was chosen for fidelity +
   simplicity, with the VM route as a documented fallback if hand-capturing all
   themes gets tedious.)
-- **Faster switches:** move `backgrounds/` out of the flake source. Diagnosis
+- ✓ **Faster switches:** move `backgrounds/` out of the flake source. Diagnosis
   (confirmed): `themes/` is 86 MB and `backgrounds/` is **all** of it — the
   palette JSONs + per-theme overrides are only ~208 KB, and the wallpapers are
   **never read at Nix eval** (only the Python `swww` path uses them). But
@@ -213,6 +213,17 @@ Design/decision records and a running log of shipped work (items marked
   Follow-on if `home-manager switch` itself is still the bottleneck after the
   copy is gone: **pre-built theme variants** (build each theme's generation
   ahead of time so a switch just activates a cached one).
+  **Shipped (2026-07-17):** Option 1, exactly as decided. New `nomarchy-wallpapers`
+  flake input (`flake = false`, its own repo, `<slug>/backgrounds/*`); a new
+  overlay derivation `nomarchy-default-themes` copies this repo's `./themes`
+  (now ~3 MB — JSONs, previews, btop/waybar/rofi overrides) and symlinks in
+  `backgrounds/` per slug from the input, failing the build if a theme JSON
+  has no matching non-empty backgrounds (drift guard, belt to
+  `check-theme-wholeswap.py`'s same assertion). `nomarchy-state-sync`'s
+  `themesDir` now points straight at that merged store path (no more
+  in-package `cp -r`) — its own closure dropped from ~94 MB to a few hundred
+  KB. `themes/*/backgrounds/` removed from this repo's working tree going
+  forward (existing git history still carries the old blobs — not rewritten).
 - Greeter (tuigreet/SDDM) theming from the same JSON (Plymouth ships since
   v1: `nomarchy.system.plymouth.*`, background tinted from the state file)
 - Installer round 2: multi-disk BTRFS RAID, impermanence, BIOS/legacy