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_campaigns.py

@@ -48,6 +48,7 @@ def create_template(
 ):
     """Create a new campaign template."""
     template = campaign_service.create_template(db, data.model_dump())
+    db.commit()
     return CampaignTemplateResponse.model_validate(template)
 
 
@@ -60,6 +61,7 @@ def update_template(
 ):
     """Update a campaign template."""
     template = campaign_service.update_template(db, template_id, data.model_dump(exclude_none=True))
+    db.commit()
     return CampaignTemplateResponse.model_validate(template)
 
 
@@ -71,6 +73,7 @@ def delete_template(
 ):
     """Delete a campaign template."""
     campaign_service.delete_template(db, template_id)
+    db.commit()
     return CampaignTemplateDeleteResponse(message="Template deleted")
 
 
@@ -98,6 +101,7 @@ def send_campaign(
         prospect_ids=data.prospect_ids,
         sent_by_user_id=current_admin.user_id,
     )
+    db.commit()
     return [CampaignSendResponse.model_validate(s) for s in sends]