Add missing copyright/license information

Author: Tino Mettler

data/website_gallery/modal.css

@@ -1,3 +1,20 @@
+/*
+    copyright (c) 2025 Tino Mettler
+
+    darktable is free software: you can redistribute it and/or modify
+    it under the terms of the GNU General Public License as published by
+    the Free Software Foundation, either version 3 of the License, or
+    (at your option) any later version.
+
+    darktable is distributed in the hope that it will be useful,
+    but WITHOUT ANY WARRANTY; without even the implied warranty of
+    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+    GNU General Public License for more details.
+
+    You should have received a copy of the GNU General Public License
+    along with this software.  If not, see <http://www.gnu.org/licenses/>.
+*/
+
 * {
     margin: 0;
     padding: 0;

data/website_gallery/modal.js

@@ -1,5 +1,20 @@
+/*
+    copyright (c) 2025 Tino Mettler
+
+    darktable is free software: you can redistribute it and/or modify
+    it under the terms of the GNU General Public License as published by
+    the Free Software Foundation, either version 3 of the License, or
+    (at your option) any later version.
+
+    darktable is distributed in the hope that it will be useful,
+    but WITHOUT ANY WARRANTY; without even the implied warranty of
+    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+    GNU General Public License for more details.
+
+    You should have received a copy of the GNU General Public License
+    along with this software.  If not, see <http://www.gnu.org/licenses/>.
+*/
 
-// DOM Elements
 const container = document.querySelector('.slide-container');
 const slides = {
     prev: document.getElementById('prev'),