refactor: migrate to eslint flat config and format codebase with prettier

- Remove legacy .eslintrc.cjs and .eslintignore
- Add eslint.config.js with flat config, security rules (no-eval, no-implied-eval, no-new-func, no-script-url)
- Add .prettierrc and .prettierignore
- Format entire codebase with prettier

.prettierignore

@@ -0,0 +1,6 @@
+dist
+node_modules
+public
+*.min.js
+*.min.css
+package-lock.json