fix: add unique() to company query with joinedload

SQLAlchemy Error Fix:
- Add .unique() when using joinedload(Company.vendors)
- When eagerly loading collection relationships with joinedload, SQLAlchemy can return duplicate rows
- The unique() method deduplicates results and is required for joined collection loads

Error was:
InvalidRequestError: The unique() method must be invoked on this Result, as it contains results that include joined eager loads against collections

This is a standard SQLAlchemy pattern for handling one-to-many relationships with eager loading.

app/services/company_service.py

@@ -157,7 +157,8 @@ class CompanyService:
         # Apply pagination and order
         query = query.order_by(Company.name).offset(skip).limit(limit)
 
-        companies = list(db.execute(query).scalars().all())
+        # Use unique() when using joinedload with collections to avoid duplicate rows
+        companies = list(db.execute(query).scalars().unique().all())
 
         return companies, total