Update Content model to enforce status choices and add migration for status field changes

- Introduced STATUS_CHOICES in the Content model to restrict the status field to 'draft', 'review', and 'published'.
- Created a new migration to reflect the updated status choices without altering existing data.
- Removed 'completed' status from the frontend status color mapping for consistency.

backend/igny8_core/modules/writer/migrations/0006_update_status_choices.py

@@ -0,0 +1,18 @@
+# Generated manually to update status field choices
+
+from django.db import migrations
+
+
+class Migration(migrations.Migration):
+
+    dependencies = [
+        ('writer', '0005_move_content_fields_to_content'),
+    ]
+
+    operations = [
+        # No database changes needed - just updating Python-level choices
+        # Tasks status: queued, completed
+        # Content status: draft, review, published
+        # Existing data will remain valid
+    ]
+