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>

pkgs/nomarchy-state-sync/default.nix

@@ -7,6 +7,10 @@
 , git
   # Shipped theme presets, baked into the package as a fallback so
   # `list`/`apply` work even when $NOMARCHY_PATH has no themes/ dir.
+  # Already a store artifact (nomarchy-default-themes merges the repo's
+  # ./themes with backgrounds/ symlinked from nomarchy-wallpapers) — the
+  # wrapper points straight at it, no copy, so it stays in the closure
+  # without duplicating it into $out.
 , themesDir ? null
 }:
 
@@ -25,17 +29,12 @@ stdenvNoCC.mkDerivation {
     install -Dm755 nomarchy-state-sync.py $out/bin/nomarchy-state-sync
     patchShebangs $out/bin/nomarchy-state-sync
 
-    ${lib.optionalString (themesDir != null) ''
-      mkdir -p $out/share/nomarchy
-      cp -r ${themesDir} $out/share/nomarchy/themes
-    ''}
-
     # Stdlib-only Python. home-manager is deliberately NOT wrapped in —
     # the rebuild must use the user's own home-manager from their PATH.
     wrapProgram $out/bin/nomarchy-state-sync \
       --prefix PATH : ${lib.makeBinPath [ awww libnotify git ]} \
       ${lib.optionalString (themesDir != null)
-        "--set NOMARCHY_DEFAULT_THEMES $out/share/nomarchy/themes"}
+        "--set NOMARCHY_DEFAULT_THEMES ${themesDir}"}
 
     # #107: old CLI name kept as a symlink so muscle memory and scripts
     # survive a pull (drop after the next stable release notes say so).