Add SNS Marketing Campaign feature

- Add cash_cc_balance to User model (withdrawable CC)
- Create SnsShareSubmission model for SNS share verification
- Add marketing campaign settings to SystemSettings
- Add reward_type to ReferralReward model
- Create /api/sns-share endpoints for submission and verification
- Add referral signup reward logic (10CC on signup)
- Create /sns-share user page for SNS sharing
- Create /admin/sns-shares management page
- Add marketing settings UI to admin settings page
- Add SNS Shares menu to admin sidebar

🤖 Generated with [Claude Code](https://claude.com/claude-code)

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

backend/app/schemas/__init__.py

@@ -47,6 +47,10 @@ from .notification import (
     NotificationCreate, NotificationResponse,
     NotificationListResponse, NotificationMarkRead,
 )
+from .sns_share import (
+    SnsShareSubmit, SnsShareResponse, SnsShareListResponse,
+    SnsShareVerify, SnsShareStats,
+)
 
 __all__ = [
     "CarMakerCreate", "CarMakerResponse",
@@ -78,4 +82,6 @@ __all__ = [
     "ReferralSettingsResponse", "ReferralSettingsUpdate",
     "NotificationCreate", "NotificationResponse",
     "NotificationListResponse", "NotificationMarkRead",
+    "SnsShareSubmit", "SnsShareResponse", "SnsShareListResponse",
+    "SnsShareVerify", "SnsShareStats",
 ]