feat: add pre-commit hooks and codecov config

[Kallyan01]

Summary

Add pre-commit hooks and Codecov configuration, bringing OneDesign onto the
shared OneSearch dev baseline. Dependabot is already configured in this repo,
so no changes were needed there.

Changes

• .lefthook.yml (new): pre-commit hook that runs lint-staged.
• .lintstagedrc.mjs (new): staged-file linting — wp-scripts lint-js --fix
  for JS/TS, wp-scripts lint-style --fix for CSS/SCSS, phpcbf for PHP, and a
  wp-scripts format pass. The PHP command is wrapped in
  sh -c "… || [ $? -eq 3 ]" so that phpcbf's exit code 3 ("fixes applied") is
  treated as success rather than failure.
• .github/.codecov.yml (new): informational project (70%) and patch (60%)
  targets, plus the fixes: path rewrite from the wp-env container path
  /var/www/html/wp-content/plugins/onedesign/ to repo-relative. Without this,
  reusable-phpunit.yml and reusable-jest.yml already upload coverage with
  CODECOV_TOKEN but no path mapping, so Codecov reports the wrong paths.
• package.json: adds prepare: lefthook install and the lefthook /
  lint-staged devDependencies. The lockfile update is purely additive
  (+239 lines, no existing dependency re-resolved).