fix(#3006): retarget PR-template CHANGELOG checkboxes at the changeset workflow (#3007)

The three PR templates still asked contributors to tick `CHANGELOG.md
updated`, contradicting the post-#2978 rule (documented in
CONTRIBUTING.md and enforced by scripts/changeset/lint.cjs) that
`CHANGELOG.md` must not be edited directly.

Each checkbox now references `npm run changeset` with the appropriate
`--type` (Fixed/Changed/Added) and notes the `no-changelog` opt-out
label where applicable, so `gh pr create` users land in the correct
workflow by copy-paste.

Closes #3006

Co-authored-by: Claude Opus 4.7 <noreply@anthropic.com>

.github/PULL_REQUEST_TEMPLATE/feature.md

@@ -94,7 +94,7 @@ Closes #
 - [ ] Implementation scope matches the approved spec exactly
 - [ ] All existing tests pass (`npm test`)
 - [ ] New tests cover the happy path, error cases, and edge cases
-- [ ] CHANGELOG.md updated with a user-facing description of the feature
+- [ ] `.changeset/` fragment added with a user-facing description of the feature (`npm run changeset -- --type Added --pr <NNN> --body "..."`)
 - [ ] Documentation updated — commands, workflows, references, README if applicable
 - [ ] No unnecessary external dependencies added
 - [ ] Works on Windows (backslash paths handled)