feat: update subscription service to use tier_id relationship

- Add get_tier_by_code and get_tier_id helper methods
- Update get_or_create_subscription to set tier_id
- Update create_subscription to set tier_id
- Update update_subscription to sync tier_id when tier changes
- Update upgrade_tier to set tier_id

All subscription CRUD operations now maintain the tier_id FK relationship
in sync with the tier code string.

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

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

app/services/subscription_service.py

@@ -28,6 +28,7 @@ from sqlalchemy.orm import Session
 from models.database.product import Product
 from models.database.subscription import (
     SubscriptionStatus,
+    SubscriptionTier,
     TIER_LIMITS,
     TierCode,
     VendorSubscription,
@@ -107,6 +108,19 @@ class SubscriptionService:
             for tier in TierCode
         ]
 
+    def get_tier_by_code(self, db: Session, tier_code: str) -> SubscriptionTier | None:
+        """Get subscription tier by code."""
+        return (
+            db.query(SubscriptionTier)
+            .filter(SubscriptionTier.code == tier_code)
+            .first()
+        )
+
+    def get_tier_id(self, db: Session, tier_code: str) -> int | None:
+        """Get tier ID from tier code. Returns None if tier not found."""
+        tier = self.get_tier_by_code(db, tier_code)
+        return tier.id if tier else None
+
     # =========================================================================
     # Subscription CRUD
     # =========================================================================
@@ -152,9 +166,13 @@ class SubscriptionService:
         now = datetime.now(UTC)
         trial_end = now + timedelta(days=trial_days)
 
+        # Lookup tier_id from tier code
+        tier_id = self.get_tier_id(db, tier)
+
         subscription = VendorSubscription(
             vendor_id=vendor_id,
             tier=tier,
+            tier_id=tier_id,
             status=SubscriptionStatus.TRIAL.value,
             period_start=now,
             period_end=trial_end,
@@ -201,9 +219,13 @@ class SubscriptionService:
             status = SubscriptionStatus.TRIAL.value
             period_end = trial_ends_at
 
+        # Lookup tier_id from tier code
+        tier_id = self.get_tier_id(db, data.tier)
+
         subscription = VendorSubscription(
             vendor_id=vendor_id,
             tier=data.tier,
+            tier_id=tier_id,
             status=status,
             period_start=now,
             period_end=period_end,
@@ -228,6 +250,12 @@ class SubscriptionService:
         subscription = self.get_subscription_or_raise(db, vendor_id)
 
         update_data = data.model_dump(exclude_unset=True)
+
+        # If tier is being updated, also update tier_id
+        if "tier" in update_data:
+            tier_id = self.get_tier_id(db, update_data["tier"])
+            update_data["tier_id"] = tier_id
+
         for key, value in update_data.items():
             setattr(subscription, key, value)
 
@@ -249,6 +277,7 @@ class SubscriptionService:
 
         old_tier = subscription.tier
         subscription.tier = new_tier
+        subscription.tier_id = self.get_tier_id(db, new_tier)
         subscription.updated_at = datetime.now(UTC)
 
         # If upgrading from trial, mark as active