chore: add husky pre-commit hook and lint-staged configuration

- Created a pre-commit hook in .husky to run lint-staged.
- Added .lintstagedrc.mjs to format frontend files with Prettier and apply Spotless to backend Java files.
- Introduced .prettierignore to exclude specific directories from formatting.

.lintstagedrc.mjs

@@ -0,0 +1,6 @@
+export default {
+	'*.{css,html,js,json,md,scss,ts,yml,yaml}':
+		'frontend/node_modules/.bin/prettier --config frontend/.prettierrc --write',
+	'backend/**/*.java': (files) =>
+		`backend/mvnw --file backend/pom.xml spotless:apply -DspotlessFiles=${files.join(',')}`,
+};