feat(FN-1714): add scope-aware scheduling and global concurrency settings

- Add scope columns (global/project) to automations table with migration v32
- Implement scope-aware store query APIs in AutomationStore and RoutineStore
- Expose global concurrency limit in Settings UI with dedicated state
- Implement null-as-delete semantics for global settings to allow explicit clearing
- Add getActiveMergingTask cross-process guard to merger for safety
- Add stale status cleanup on startup sweep for crash recovery
- Update mock store in merger tests to include getActiveMergingTask method

packages/engine/src/merger.test.ts

@@ -118,6 +118,7 @@ function createMockStore(taskOverrides: Partial<Task> = {}, allTasks: Task[] = [
     appendAgentLog: vi.fn().mockResolvedValue(undefined),
     updateSettings: vi.fn().mockResolvedValue({}),
     getSettings: vi.fn().mockResolvedValue({ ...DEFAULT_SETTINGS }),
+    getActiveMergingTask: vi.fn().mockReturnValue(null),
     emit: vi.fn(),
     on: vi.fn(),
   } as unknown as TaskStore;