docs: update CONTRIBUTING.md with lint and test steps, remove duplicate PR template

.github/PULL_REQUEST_TEMPLATE.md

@@ -1,25 +0,0 @@
-## Description
-
-<!-- What does this PR do? Why is it needed? -->
-
-## Type of Change
-
-- [ ] 🐛 Bug fix
-- [ ] ✨ New feature
-- [ ] 💅 Style / UI change
-- [ ] ♻️ Refactor (no behavior change)
-- [ ] 📝 Documentation
-- [ ] 🧪 Tests
-- [ ] 🔧 Build / CI / tooling
-
-## Checklist
-
-- [ ] `npm run build` passes with zero errors
-- [ ] Tested in browser (dev server or production build)
-- [ ] Commit messages follow [Conventional Commits](https://www.conventionalcommits.org/)
-- [ ] No secrets or credentials included
-- [ ] Translations updated in `src/lib/i18n.ts` if UI text changed
-
-## Screenshots
-
-<!-- If this changes the UI, add before/after screenshots or a short GIF -->