test(git-sync): mock db.transaction in movePage provenance specs

After rebasing onto develop, movePage runs its cycle-check + UPDATE inside
executeTx(this.db) (develop #207 advisory-lock/atomic cycle-guard). The
git-sync provenance specs still passed a bare `{}` db, so executeTx hit
`db.transaction is not a function`. Reuse the same trxStub Proxy + transaction
mock the develop movePage specs use so both the advisory-lock `sql.execute(trx)`
and updatePage resolve. Production movePage keeps BOTH develop's lock/cycle
guard AND git-sync's provenance stamping; this only updates the test harness.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

apps/server/src/core/page/services/page.service.spec.ts

@@ -653,11 +653,27 @@ describe('PageService', () => {
         };
         const eventEmitter = { emit: jest.fn() };
 
+        // movePage now runs the cycle-check + UPDATE inside executeTx(this.db),
+        // i.e. this.db.transaction().execute(fn => fn(trx)). A permissive
+        // chainable Proxy stands in for the Kysely trx so the per-space
+        // advisory-lock `sql``.execute(trx)` resolves and updatePage runs.
+        const trxStub: any = new Proxy(function () {}, {
+          get: (_t, p) =>
+            p === 'then'
+              ? undefined
+              : p === 'execute' || p === 'executeTakeFirst'
+                ? () => Promise.resolve([])
+                : () => trxStub,
+        });
+        const db = {
+          transaction: () => ({ execute: (fn: any) => fn(trxStub) }),
+        };
+
         const svc = new PageService(
           pageRepo as any, // pageRepo
           {} as any, // pagePermissionRepo
           {} as any, // attachmentRepo
-          {} as any, // db
+          db as any, // db
           {} as any, // storageService
           {} as any, // attachmentQueue
           {} as any, // aiQueue