refactor(prospecting): migrate SVC-006 transaction control to endpoint level

Move db.commit() from services to API endpoints and Celery tasks.
Services now use db.flush() only; endpoints own the transaction.

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

app/modules/prospecting/routes/api/admin_interactions.py

@@ -51,6 +51,7 @@ def create_interaction(
         user_id=current_admin.user_id,
         data=data.model_dump(exclude_none=True),
     )
+    db.commit()
     return InteractionResponse.model_validate(interaction)