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

.prettierrc

@@ -0,0 +1,13 @@
+{
+  "semi": true,
+  "singleQuote": true,
+  "tabWidth": 2,
+  "useTabs": false,
+  "trailingComma": "all",
+  "printWidth": 100,
+  "bracketSpacing": true,
+  "arrowParens": "always",
+  "endOfLine": "auto",
+  "jsxSingleQuote": false,
+  "plugins": ["prettier-plugin-tailwindcss"]
+}