feat(migrate): ensureSpace helper

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

migrate/spaces.js

@@ -0,0 +1,12 @@
+import { pool } from '../lib/db/pool.js';
+import * as spaces from '../lib/db/repos/spaces.js';
+
+const SYS = { kind: 'system', id: null };
+
+// Returns the id of the space with `slug`, creating it if absent. Idempotent.
+export async function ensureSpace(slug, name) {
+  const { rows: [r] } = await pool.query(`SELECT id FROM spaces WHERE slug=$1`, [slug]);
+  if (r) return r.id;
+  const created = await spaces.create({ slug, name }, SYS);
+  return created.id;
+}