chore: add reuse licence checking (#6659)

This PR aims to add very basic REUSE license checking
https://reuse.software.

My intention is not to sort out all errors in this PR, but instead sort
that out over multiple incrementals PR going forward in an undisruptive
way as possible.

REUSE.toml

@@ -0,0 +1,26 @@
+# SPDX-FileCopyrightText: 2025 Rasmus Karlsson <rasmus.karlsson@pajlada.com>
+# SPDX-License-Identifier: CC0-1.0
+
+version = 1
+SPDX-PackageName = "chatterino"
+SPDX-PackageDownloadLocation = "https://chatterino.com/"
+
+# [[annotations]]
+# License files we embed for display to users
+# XXX: How do we license these?
+# path = "resources/licenses/*.txt"
+
+# [[annotations]]
+# # These files are part of code generation for the Twitch EventSub WebSocket library.
+# path = "lib/twitch-eventsub-ws/include/twitch-eventsub-ws/payloads/*.inc"
+# SPDX-FileCopyrightText = "Contributors to Chatterino <https://chatterino.com>"
+# SPDX-License-Identifier = "MIT"
+#
+# [[annotations]]
+# # Snapshot tests
+# path = [
+#     "tests/snapshots/**",
+#     "lib/twitch-eventsub-ws/tests/resources/**.json",
+# ]
+# SPDX-FileCopyrightText = "Contributors to Chatterino <https://chatterino.com>"
+# SPDX-License-Identifier = "CC0-1.0"