Fix subscriptions page including income transactions

Salary and other income marked is_recurring=True were being returned
alongside expense subscriptions. Added type='expense' filter so only
outgoing recurring transactions appear.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

backend/app/api/v1/subscriptions.py

@@ -34,6 +34,7 @@ async def get_subscriptions(
         select(Transaction).where(
             Transaction.user_id == user.id,
             Transaction.is_recurring == True,
+            Transaction.type == "expense",
             Transaction.deleted_at.is_(None),
         )
     )