✨ feat(frontend): quiz bonus post-contact (Story 4.9)

- Add BonusQuiz.vue component with 7 randomized questions
- Add challenge-bonus.vue page with intro, quiz, and results
- Redirect to bonus quiz after successful contact form submission
- Add i18n translations for bonus.* (fr/en)

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

frontend/i18n/en.json

@@ -320,5 +320,24 @@
     "successMessage": "Thanks for your message. I'll get back to you as soon as possible.",
     "error": "An error occurred. Please try again later.",
     "rateLimitError": "Too many attempts. Please wait a moment before trying again."
+  },
+  "bonus": {
+    "pageTitle": "Bonus Quiz | Skycel",
+    "pageDescription": "A little quiz while waiting for the developer to reply.",
+    "exit": "Exit",
+    "waitingTitle": "Message sent!",
+    "waitingMessage": "While the developer finds their way to the inbox... a little quiz to pass the time?",
+    "playQuiz": "Play the quiz",
+    "noThanks": "No thanks, I'm done",
+    "question": "Question",
+    "correct": "Correct!",
+    "incorrect": "Not quite...",
+    "resultTitle": "Quiz completed!",
+    "perfectMessage": "Perfect score! You really know web development... and Celian!",
+    "goodMessage": "Well done! You have solid web development basics.",
+    "tryMessage": "Keep learning! Web development is an endless journey.",
+    "playAgain": "Play again",
+    "backHome": "Back to home",
+    "messageConfirm": "Your message was sent successfully. Celian will reply soon!"
   }
 }