feat: Implement full-stack course announcements management with cohort segmentation.

services/cms-service/migrations/20260219000001_course_teams.sql

@@ -0,0 +1,17 @@
+-- Migration to support multiple instructors per course
+CREATE TABLE course_instructors (
+    id UUID PRIMARY KEY DEFAULT gen_random_uuid(),
+    course_id UUID NOT NULL REFERENCES courses(id) ON DELETE CASCADE,
+    user_id UUID NOT NULL REFERENCES users(id) ON DELETE CASCADE,
+    role TEXT NOT NULL DEFAULT 'instructor', -- 'primary', 'instructor', 'assistant'
+    created_at TIMESTAMPTZ NOT NULL DEFAULT NOW(),
+    UNIQUE(course_id, user_id)
+);
+
+-- Seed with existing data from courses table
+INSERT INTO course_instructors (course_id, user_id, role)
+SELECT id, instructor_id, 'primary' FROM courses;
+
+-- We keep the instructor_id in courses for now to avoid breaking changes, 
+-- but it should be considered deprecated in favor of course_instructors.
+COMMENT ON COLUMN courses.instructor_id IS 'Deprecated: use course_instructors table instead.';