Adjust Debian Edu legacy artwork to Debian (Edu) 13.

[ Reason ]
Targetting the first RC release of Debian Edu based on Debian 13 we need
to adjust debian-edu-artwork-legacy to match recent changes in
desktop-base and branded components.

[ Impact ]
Broken spacefun Debian Edu artwork (which is shipped in this src:pkg).

[ Tests ]
Customer-provided version of this package is in use since autumn 2025.

[ Risks ]
Only for Debian Edu users, only for those who install this nice
(spacefun) artwork theme.

[ Checklist ]
  [x] *all* changes are documented in the d/changelog
  [x] I reviewed all changes and I approve them
  [x] attach debdiff against the package in (old)stable
  [x] the issue is verified as fixed in unstable

[ Changes ]

```
--- debian-edu-artwork-legacy-20220131/debian/changelog	2022-01-31 13:45:54.000000000 +0100
+++ debian-edu-artwork-legacy-20250915/debian/changelog	2026-09-07 14:12:17.000000000 +0200
@@ -1,3 +1,50 @@
+debian-edu-artwork-legacy (20250915-3~deb13u1) trixie; urgency=medium
+
+  * Release to trixie.
+
+ -- Mike Gabriel <sunweaver@debian.org>  Mon, 07 Sep 2026 14:12:17 +0200
+
+debian-edu-artwork-legacy (20250915-3) unstable; urgency=medium
+
+  * debian/debian-edu-artwork-spacefun.install:
+    + Re-add lost +usr/share/gnome-background-properties/. (Regression fix).
+
+ -- Mike Gabriel <sunweaver@debian.org>  Mon, 15 Sep 2025 14:28:09 +0200
+
+debian-edu-artwork-legacy (20250915-2) unstable; urgency=medium
+
+  * Integrate changes from NMU 20220131-1.1.
+
+ -- Mike Gabriel <sunweaver@debian.org>  Mon, 15 Sep 2025 14:19:25 +0200
+
+debian-edu-artwork-legacy (20250915-1) unstable; urgency=medium
+
+  * art-spacefun/arctica-greeter/34_arctica-greeter-theme-debian-edu-artwork-
+    spacefun.gschema.override:
+    + Add file. Hide the Debian (Edu) logo in arctica-greeter and use the
+      background.svg (instead of the background-nologo.svg).
+  * debian/debian-edu-artwork-spacefun.triggers:
+    + Add /usr/share/doc/debian-edu-artwork-spacefun to d-e-a-spacefun triggers.
+  * debian/update-debian-edu-artwork-spacefun*:
+    + Copy new script version from d-e-artwork src:pkg, also use their homepage
+      template.
+  * debian/{compat,control,rules}:
+    + Port to pure debhelper.
+  * debian/control:
+    + Bump Standards-Version: to 4.7.2. No changes needed.
+  * debian/copyright:
+    + Update copyright attributions.
+    + Update FSF mailing address.
+
+ -- Mike Gabriel <sunweaver@debian.org>  Mon, 15 Sep 2025 12:47:01 +0200
+
+debian-edu-artwork-legacy (20220131-1.1) unstable; urgency=medium
+
+  * Non-maintainer upload.
+  * Drop usage of CDBS
+
+ -- Alexandre Detiste <tchet@debian.org>  Mon, 08 Sep 2025 23:15:24 +0200
+
 debian-edu-artwork-legacy (20220131-1) unstable; urgency=medium

   * art-spacefun/desktop-base/grub-16x9.png:
```

[ Other info ]
This upload to trixie is part of the first release candidate of Debian Edu based on Debian 13.