feat(security,quality): implement security and code quality optimizations

Phase 6: Security Optimizations
- Install DOMPurify for XSS protection
- Create sanitize utilities (HTML, input, URL, escape)
- Implement input sanitization in contact form
- Add CSRF token generation and validation
- Integrate CSRF protection in form submissions

Phase 7: Code Quality Optimizations
- Enhance TypeScript strict mode configuration
- Add noUncheckedIndexedAccess for safer array access
- Enable noImplicitReturns and noFallthroughCasesInSwitch
- Add noUnusedLocals and noUnusedParameters
- Enable exactOptionalPropertyTypes for precise types
- Configure comprehensive ESLint rules
- Add React security rules (no-unescaped-entities, jsx-no-target-blank)
- Add TypeScript best practices rules
- Add code quality rules (prefer-const, eqeqeq, curly)

Files modified:
- package.json: Add DOMPurify dependency
- src/lib/sanitize.ts: New sanitization utilities
- src/lib/csrf.ts: New CSRF protection utilities
- src/components/sections/contact-section.tsx: Security integration
- tsconfig.json: Enhanced TypeScript configuration
- eslint.config.mjs: Comprehensive ESLint rules

Impact:
- XSS attack prevention
- CSRF attack prevention
- Better type safety
- Improved code quality
- Financial-grade security standards

eslint.config.mjs

@@ -5,14 +5,38 @@ import nextTs from "eslint-config-next/typescript";
 const eslintConfig = defineConfig([
   ...nextVitals,
   ...nextTs,
-  // Override default ignores of eslint-config-next.
   globalIgnores([
-    // Default ignores of eslint-config-next:
     ".next/**",
     "out/**",
     "build/**",
     "next-env.d.ts",
   ]),
+  {
+    rules: {
+      "react/no-unescaped-entities": "error",
+      "react/jsx-no-target-blank": "error",
+      "react/jsx-curly-brace-presence": ["error", { "props": "never", "children": "never" }],
+      "react/self-closing-comp": "error",
+      "react/jsx-boolean-value": ["error", "never"],
+      "@typescript-eslint/no-unused-vars": ["error", { 
+        "argsIgnorePattern": "^_",
+        "varsIgnorePattern": "^_" 
+      }],
+      "@typescript-eslint/explicit-function-return-type": "off",
+      "@typescript-eslint/no-explicit-any": "warn",
+      "@typescript-eslint/prefer-nullish-coalescing": "error",
+      "@typescript-eslint/prefer-optional-chain": "error",
+      "@typescript-eslint/no-unnecessary-condition": "warn",
+      "no-console": ["warn", { "allow": ["warn", "error"] }],
+      "prefer-const": "error",
+      "no-var": "error",
+      "eqeqeq": ["error", "always"],
+      "curly": ["error", "all"],
+      "no-throw-literal": "error",
+      "no-return-await": "error",
+      "prefer-promise-reject-errors": "error",
+    },
+  },
 ]);
 
 export default eslintConfig;