feat: Add Review (사용후기) board system with CC reward

- Backend: Review model, full API (public/user/admin endpoints)
- Frontend: list, detail, write/edit pages, admin management
- 1 CC reward for writing a review on completed vehicle requests
- Navigation updates (Header + admin sidebar)
- "Write Review" button on my-request page for completed requests

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

backend/app/models/__init__.py

@@ -19,6 +19,7 @@ from .exchange_rate import ExchangeRate, ExchangeRateHistory
 from .cc_package import CCPackage, DEFAULT_CC_PACKAGES
 from .visitor import VisitorLog, VisitorDailyStats, VisitorSession
 from .bulletin import BoardCategory, BoardPost
+from .review import Review
 
 __all__ = [
     "CarMaker",
@@ -66,4 +67,5 @@ __all__ = [
     "VisitorSession",
     "BoardCategory",
     "BoardPost",
+    "Review",
 ]