chore: improve PR template & request AI usage disclosure

Author: chrisgrieser

.github/pull_request_template.md

@@ -1,9 +1,16 @@
-## What problem does this PR solve?
+## Problem statement
+<!-- Briefly describe the issue this PR addresses. -->
 
-## How does the PR solve it?
+## Proposed solution
+<!-- Explain how this PR resolves the problem. -->
+
+## AI usage disclosure
+<!-- If you used AI beyond simple autocomplete, describe how. 
+AI-assisted code is not discouraged if it has been properly reviewed; 
+this disclosure is for transparency. -->
 
 ## Checklist
-- [ ] Used only `camelCase` variable names.
-- [ ] If functionality is added or modified, also made respective changes to the
-  `README.md` (the `.txt` file is auto-generated and does not need to be
-  modified).
+- [ ] Variable names follow `camelCase` convention.
+- [ ] All AI-generated code has been reviewed by a human.
+- [ ] The `README.md` has been updated for any new or modified functionality
+  (the `.txt` file is auto-generated and does not need to be modified).