feat(assign): let leads manually assign operators + sync Jira; send platform as Jira label

Adds GET /users/operators (leads+admin) and wires a lead-only assign
control into the test detail header, calling the existing but
previously unreachable POST /tests/{id}/assign endpoint. Manual
assignment now also pushes the Jira ticket assignee immediately
instead of waiting for the operator to start execution.

Also adds test.platform as a kebab-case label on Jira ticket creation.

frontend/src/api/tests.ts

@@ -179,6 +179,15 @@ export async function updateTestClassification(
   return data;
 }
 
+/** Assign red_tech/blue_tech operators to a test (leads + admin only). */
+export async function assignTestOperators(
+  testId: string,
+  payload: { red_tech_assignee?: string | null; blue_tech_assignee?: string | null },
+): Promise<Test> {
+  const { data } = await client.post<Test>(`/tests/${testId}/assign`, payload);
+  return data;
+}
+
 // ── Red Team ───────────────────────────────────────────────────────
 
 /** Red Team updates their fields (draft, red_executing). */