chore(setup): use Apache 2.0 boilerplate header

setup.py

@@ -1,6 +1,19 @@
 #!/usr/bin/env python3
-# SPDX-FileCopyrightText: 2026 Oscar Wallberg
+#
-# SPDX-License-Identifier: Apache-2.0
+# Copyright 2026 Oscar Wallberg
+#
+# Licensed under the Apache License, Version 2.0 (the "License");
+# you may not use this file except in compliance with the License.
+# You may obtain a copy of the License at
+#
+#     http://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS IS" BASIS,
+# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+# See the License for the specific language governing permissions and
+# limitations under the License.
+
 """Install dotfiles and system configuration from this repo."""
 
 from __future__ import annotations