fix: correct imports in admin subscriptions module

- Use get_current_admin_api instead of non-existent get_current_admin
- Use get_db from app.core.database
- Replace generic NotFoundException with specific exceptions:
  - TierNotFoundException for tier lookup failures
  - ConflictException for duplicate tier codes
  - BusinessLogicException for tier deletion with active subscriptions
  - ResourceNotFoundException for subscription lookup failures

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

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

app/services/admin_subscription_service.py

@@ -15,7 +15,12 @@ from math import ceil
 from sqlalchemy import func
 from sqlalchemy.orm import Session
 
-from app.exceptions import NotFoundException
+from app.exceptions import (
+    BusinessLogicException,
+    ConflictException,
+    ResourceNotFoundException,
+    TierNotFoundException,
+)
 from models.database.subscription import (
     BillingHistory,
     SubscriptionStatus,
@@ -54,7 +59,7 @@ class AdminSubscriptionService:
         )
 
         if not tier:
-            raise NotFoundException(f"Tier '{tier_code}' not found")
+            raise TierNotFoundException(tier_code)
 
         return tier
 
@@ -67,7 +72,7 @@ class AdminSubscriptionService:
             .first()
         )
         if existing:
-            raise NotFoundException(
+            raise ConflictException(
                 f"Tier with code '{tier_data['code']}' already exists"
             )
 
@@ -107,7 +112,7 @@ class AdminSubscriptionService:
         )
 
         if active_subs > 0:
-            raise NotFoundException(
+            raise BusinessLogicException(
                 f"Cannot delete tier: {active_subs} active subscriptions are using it"
             )
 
@@ -172,7 +177,7 @@ class AdminSubscriptionService:
         )
 
         if not result:
-            raise NotFoundException(f"Subscription for vendor {vendor_id} not found")
+            raise ResourceNotFoundException(f"Subscription for vendor {vendor_id} not found")
 
         return result