feat: credit-based billing system

- New DB models: credit_packages, subscription_plans, user_credits, credit_consumptions, credit_purchases
- CreditService: balance, deduct, add_credits, grant_free_trial, history
- User API: /api/v1/credits/* (balance/history/packages/purchase/subscribe)
- Admin API: /api/v1/admin/credit-* (CRUD packages/plans, user credits, consumptions)
- PaymentService.create_credit_order + handle_callback for credit purchases
- Credit deduction on: discovery, translate, marketing, ai_chat, followup
- Free trial 30 credits on registration
- Documentation: docs/CREDIT_SYSTEM.md

backend/app/api/v1/marketing.py

@@ -5,6 +5,7 @@ from sqlalchemy.ext.asyncio import AsyncSession
 from app.database import get_db
 from app.services.marketing import MarketingService
 from app.services.preference import UserPreferenceService
+from app.services.credit import CreditService
 from app.core.security import decode_token
 from app.api.v1.deps import get_current_user_id
 from app.config import settings
@@ -45,6 +46,14 @@ async def generate_marketing(
     user_id: str = Depends(get_current_user_id),
     db: AsyncSession = Depends(get_db),
 ):
+    credit_svc = CreditService(db)
+    ok, balance = await credit_svc.deduct(user_id, "marketing_content")
+    if not ok:
+        raise HTTPException(
+            status_code=402,
+            detail=f"次数不足 (剩余 {balance:.1f}, 需要 5)"
+        )
+
     service = MarketingService()
     pref_service = UserPreferenceService(db)
     pref_context = await pref_service.get_preference_context(user_id, "marketing")
@@ -63,6 +72,7 @@ async def generate_marketing(
         "product": data.product_name,
         "target": data.target,
         "count": len(results),
+        "credits_remaining": balance - 5,
     }
 
 
@@ -70,7 +80,16 @@ async def generate_marketing(
 async def generate_keywords(
     data: KeywordsRequest,
     user_id: str = Depends(get_current_user_id),
+    db: AsyncSession = Depends(get_db),
 ):
+    credit_svc = CreditService(db)
+    ok, balance = await credit_svc.deduct(user_id, "marketing_content")
+    if not ok:
+        raise HTTPException(
+            status_code=402,
+            detail=f"次数不足 (剩余 {balance:.1f}, 需要 5)"
+        )
+
     service = MarketingService()
     product_info = {
         "name": data.product_name,
@@ -79,14 +98,23 @@ async def generate_keywords(
     }
     keywords = await service.generate_keywords(product_info, data.language, data.count)
 
-    return {"keywords": keywords, "product": data.product_name}
+    return {"keywords": keywords, "product": data.product_name, "credits_remaining": balance - 5}
 
 
 @router.post("/competitor-analysis")
 async def competitor_analysis(
     data: CompetitorRequest,
     user_id: str = Depends(get_current_user_id),
+    db: AsyncSession = Depends(get_db),
 ):
+    credit_svc = CreditService(db)
+    ok, balance = await credit_svc.deduct(user_id, "competitor_analysis")
+    if not ok:
+        raise HTTPException(
+            status_code=402,
+            detail=f"次数不足 (剩余 {balance:.1f}, 需要 10)"
+        )
+
     service = MarketingService()
     product_info = {
         "name": data.product_name,
@@ -95,4 +123,4 @@ async def competitor_analysis(
     }
     analysis = await service.analyze_competitors(product_info, data.market)
 
-    return {"analysis": analysis, "product": data.product_name, "market": data.market}
+    return {"analysis": analysis, "product": data.product_name, "market": data.market, "credits_remaining": balance - 10}