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/models/user.py

@@ -24,7 +24,8 @@ class User(Base):
     is_active = Column(Boolean, default=True)
     is_admin = Column(Boolean, default=False)
     is_dealer = Column(Boolean, default=False)  # Dealer status
-    cc_balance = Column(Float, default=3.0)  # CC coin balance, 3 free on signup
+    cc_balance = Column(Float, default=3.0)  # 프로모션 CC (출금 불가) - 가입보너스, SNS공유, 레퍼럴
+    cash_cc_balance = Column(Float, default=0.0)  # 현금성 CC (출금 가능) - 딜러수수료 88%
     referral_code = Column(String(8), unique=True, index=True)  # Unique referral code for sharing
     referred_by = Column(String(8), nullable=True)  # Referral code of the user who referred this user