🛡️ Sentinel: [HIGH] Implement strict email validation

- Implemented `isValidEmail` utility with strict regex validation (rejects `<` and `>`) to prevent XSS vectors.
- Updated `Contact.tsx` to use `isValidEmail` instead of weak regex.
- Added comprehensive tests for `isValidEmail` in `src/utils/security.test.ts`.
- Fixed flaky test in `src/pages/__tests__/Contact.test.tsx` by clearing `localStorage` in `afterEach`.
- Added test case for invalid email submission.
- Documented findings in `.jules/sentinel.md`.

Co-authored-by: ragusa-it <196988693+ragusa-it@users.noreply.github.com>

src/pages/Contact.tsx

@@ -5,7 +5,7 @@ import { useTranslation } from "../i18n";
 import { useRateLimit } from "../hooks";
 import { config } from "../config";
 import { Button, Input, Textarea } from "../components/ui";
-import { sanitizeInput } from "../utils/security";
+import { sanitizeInput, isValidEmail } from "../utils/security";
 import styles from "./Contact.module.css";
 
 const NAME_MAX_LENGTH = 100;
@@ -53,7 +53,7 @@ export function Contact() {
 
     if (!formData.email.trim()) {
       newErrors.email = "Required";
-    } else if (!/^[^\s@]+@[^\s@]+\.[^\s@]+$/.test(formData.email)) {
+    } else if (!isValidEmail(formData.email)) {
       newErrors.email = "Invalid email";
     }