chore: enforce pre-PR validation (aggregate scripts, git hooks, PR checklist) (#1061)

* chore: enforce pre-PR validation with aggregate scripts, git hooks, and PR checklist

Add tooling to help contributors run the same checks as CI before
submitting a pull request, reducing avoidable format/lint/build failures.

- Add aggregate npm scripts:
  - `npm run check` runs format-check + lint + build + test (mirrors CI)
  - `npm run fix` runs format + lint:fix + build
- Add husky + lint-staged git hooks (installed via `npm install`):
  - pre-commit formats and lints staged files
  - pre-push rebuilds dist/ and runs the test suite
- Add a checklist item to the PR template prompting contributors to run
  `npm run check` locally
- Document the aggregate scripts and hooks in docs/contributors.md

dist/ is intentionally not auto-committed by CI to avoid pwn-request
security risks; the existing `Check dist/` workflow continues to verify it.

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

* Apply suggestions from code review

Co-authored-by: Copilot Autofix powered by AI <175728472+Copilot@users.noreply.github.com>

---------

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>
Co-authored-by: Copilot Autofix powered by AI <175728472+Copilot@users.noreply.github.com>

.github/pull_request_template.md

@@ -5,5 +5,6 @@ Describe your changes.
 Add link to the related issue.
 
 **Check list:**
+- [ ] Ran `npm run check` locally (format, lint, build, test) and all checks pass.
 - [ ] Mark if documentation changes are required.
 - [ ] Mark if tests were added or updated to cover the changes.