docs(licensing): add SPDX headers

Add SPDX copyright and license markers to repository metadata and
documentation files.

Use comment styles appropriate for git attributes, gitignore, the commit
message template, README, and justfile so license metadata is visible
without changing runtime behavior.

1 files changed, 4 insertions, 0 deletions

diff --git a/justfile b/justfile
index 27bb985..40f294f 100644
--- a/justfile
+++ b/justfile
@@ -1,3 +1,7 @@
+# SPDX-FileCopyrightText: 2026 Dennis Fink <me+coding@dennisfink.me>
+#
+# SPDX-License-Identifier: BSD-3-Clause
+
 set shell := ["bash", "-eu", "-o", "pipefail", "-c"]
 
 default: