fix: Fetch remote before merge/push in initiative approval

approveInitiative was merging and pushing with a stale local
defaultBranch, causing "rejected (fetch first)" when origin/main
had advanced since the last project sync. Now fetches remote and
fast-forwards the target branch before merging.

apps/server/execution/orchestrator.test.ts

@@ -49,6 +49,8 @@ function createMocks() {
     getMergeBase: vi.fn().mockResolvedValue('abc123'),
     pushBranch: vi.fn(),
     checkMergeability: vi.fn().mockResolvedValue({ mergeable: true }),
+    fetchRemote: vi.fn(),
+    fastForwardBranch: vi.fn(),
   };
 
   const phaseRepository = {