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

package.json

@@ -15,6 +15,7 @@
     "@types/three": "^0.183.1",
     "class-variance-authority": "^0.7.1",
     "clsx": "^2.1.1",
+    "dompurify": "^3.3.1",
     "framer-motion": "^12.34.3",
     "lucide-react": "^0.563.0",
     "next": "16.1.6",
@@ -26,6 +27,7 @@
   },
   "devDependencies": {
     "@tailwindcss/postcss": "^4",
+    "@types/dompurify": "^3.0.5",
     "@types/node": "^20",
     "@types/react": "^19",
     "@types/react-dom": "^19",