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.

frontend/src/api/campaigns.ts

@@ -134,8 +134,12 @@ export async function removeTestFromCampaign(
 }
 
 /** Activate a campaign. */
-export async function activateCampaign(campaignId: string): Promise<Campaign> {
-  const { data } = await client.post<Campaign>(`/campaigns/${campaignId}/activate`);
+export async function activateCampaign(
+  campaignId: string,
+  options?: { force?: boolean },
+): Promise<Campaign> {
+  const params = options?.force ? "?force=true" : "";
+  const { data } = await client.post<Campaign>(`/campaigns/${campaignId}/activate${params}`);
   return data;
 }