chore: Drop dead collaborativeEditing column from teams (#12669)

The collaborativeEditing toggle has been unused since collaborative
editing became always-on. The column is no longer defined in the Team
model nor referenced anywhere in the codebase, so this drops it.

Co-authored-by: Claude Opus 4.8 <noreply@anthropic.com>

server/migrations/20260611000000-drop-team-collaborative-editing.js

@@ -0,0 +1,14 @@
+"use strict";
+
+/** @type {import('sequelize-cli').Migration} */
+module.exports = {
+  async up(queryInterface) {
+    await queryInterface.removeColumn("teams", "collaborativeEditing");
+  },
+
+  async down(queryInterface, Sequelize) {
+    await queryInterface.addColumn("teams", "collaborativeEditing", {
+      type: Sequelize.BOOLEAN,
+    });
+  },
+};