fix: 接入备份维护钩子并补齐 SQLX 缓存

- ProcessManager 新增 has_instance_process（备份启动守卫依赖）

- 删除/启动/编辑/迁移目录时接入备份维护钩子（lock_instance_maintenance + begin_instance_deletion + delete_instance_backups），remove_instance 拆出 remove_instance_files_and_state

- run 启动前检查活跃备份操作并加维护锁

- 目录迁移时搬移默认备份仓库并入队清理

- 更新 settings SELECT 的 SQLX 离线缓存（补 ui_font/backup_repository_path/mono_font）

- create_recorded_symlink 非 Windows 未用参数加 cfg_attr 豁免

packages/app-lib/src/state/process.rs

@@ -533,6 +533,13 @@ impl ProcessManager {
             .collect()
     }
 
+    /// Whether any tracked process belongs to the given instance.
+    pub fn has_instance_process(&self, instance_id: &str) -> bool {
+        self.processes
+            .iter()
+            .any(|entry| entry.value().metadata.instance_id == instance_id)
+    }
+
     pub fn try_wait(
         &self,
         id: Uuid,