chore: add pull request template (#502)

.github/pull_request_template.md

@@ -0,0 +1,21 @@
+<!--
+Hey there, thanks for contributing to Heretic!
+
+Please provide a 100% HUMAN-WRITTEN description of the contents and purpose of this pull request.
+Use the [Conventional Commits](https://www.conventionalcommits.org/en/v1.0.0/) format for the pull request title.
+Link to any relevant issues or other pull requests in the description.
+
+Do NOT write the description using an LLM, not even partially.
+I am a human and reviewing pull requests takes a lot of human effort.
+I expect to communicate with the human posting the PR, not with their agent.
+Please do not open a PR if you aren't prepared to respond to comments yourself.
+-->
+
+
+### AI use declaration
+
+Check *either* of the following:
+
+- [ ] I wrote the code in this PR entirely by myself.
+- [ ] I used AI to write some or all of the code in this PR, **and** I have reviewed the entire code myself
+      and fully understand it. I'm prepared to discuss the code without letting an agent speak on my behalf.