docs: require changelog entries for user-visible changes

.github/PULL_REQUEST_TEMPLATE.md

@@ -5,6 +5,7 @@
 - [ ] I'm requesting to **pull a topic/feature/bugfix branch**.
 - [ ] I checked that my code additions will pass code linting checks and unit tests.
 - [ ] I updated unit and integration tests (if applicable).
+- [ ] I added an `[Unreleased]` changelog entry for a user-visible change, or confirmed the change is exempt.
 - [ ] I'm ready to notify the team of this contribution.
 
 ### Description

CONTRIBUTING.md

@@ -24,6 +24,10 @@ Please note that this project is released with a [Code of Conduct](./CODE_OF_CON
 	* `pyproject.toml` should have comments for non-obvious settings
 	* Unit tests should have clear names and docstrings
 	* Integration tests should document their scenarios
+- **Changelog**: User-visible features, fixes, deprecations, and behavior changes
+  must add a concise entry under the appropriate heading in `[Unreleased]` in
+  [`CHANGELOG.md`](./CHANGELOG.md). Documentation-only changes, tests, internal
+  refactors, and CI/tooling changes that do not affect users are exempt.
 - **Code Style**: We follow PEP 8 conventions. Use `ruff` for formatting and linting. Run `uv run ruff check .` and `uv run ruff format --check .` to check compliance
 
 #### Review SLAs