fix(campaigns): start_date modal + hide future-campaign tests from queue

Backend: activate endpoint returns 409 with structured warning when
start_date is in the future; accepts force=true to bypass.
test_crud_service: always excludes tests from draft campaigns with future
start_date so they do not appear in the team queue prematurely.

Frontend: catches 409 on activate and shows amber confirmation modal
with Keep scheduled / Activate now anyway options.

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

backend/app/routers/campaigns.py

@@ -273,28 +273,33 @@ def remove_test_from_campaign(
 @router.post("/{campaign_id}/activate")
 def activate_campaign(
     campaign_id: str,
+    force: bool = Query(False, description="Activate even if start_date is in the future"),
     db: Session = Depends(get_db),
     current_user: User = Depends(require_any_role("red_lead", "blue_lead")),
 ):
     """Activate a campaign, moving it from draft to active.
 
-    If the campaign has a start_date in the future, manual activation is blocked —
-    the campaign will be auto-activated by the scheduler when the date arrives.
+    If the campaign has a start_date in the future and force=False, returns a 409
+    with a warning so the frontend can show a confirmation modal. If force=True,
+    activates immediately regardless of start_date.
     """
-    # Guard: start_date must have been reached before manual activation
+    from fastapi import HTTPException
     campaign_obj = db.query(Campaign).filter(Campaign.id == campaign_id).first()
-    if campaign_obj and campaign_obj.start_date:
+    if campaign_obj and campaign_obj.start_date and not force:
         now = datetime.utcnow()
         if campaign_obj.start_date > now:
-            from fastapi import HTTPException
             raise HTTPException(
-                status_code=422,
-                detail=(
-                    f"This campaign is scheduled to start on "
-                    f"{campaign_obj.start_date.strftime('%Y-%m-%d')}. "
-                    f"It will be activated automatically on that date. "
-                    f"To activate it now, remove the start date first."
-                ),
+                status_code=409,
+                detail={
+                    "code": "start_date_in_future",
+                    "start_date": campaign_obj.start_date.strftime("%Y-%m-%d"),
+                    "message": (
+                        f"This campaign is scheduled to start on "
+                        f"{campaign_obj.start_date.strftime('%d %b %Y')}. "
+                        f"It will activate automatically on that date. "
+                        f"Do you want to activate it now anyway?"
+                    ),
+                },
             )
 
     with UnitOfWork(db) as uow: