refactor: 拆分 gateway 单体为独立 crate，新增 systemd 部署方案

将 gateway 内部的 model-fetch、provider-transport、scheduler-core、
usage-runtime、video-tasks-core 模块提取为独立 crate；重构 gateway
内部模块结构（state/router/cache/data/query 等）；移除大量遗留模块
文件；新增 systemd 二进制部署骨架及相关文档；更新前端 usage 相关
API 和组件。

crates/aether-video-tasks-core/src/store.rs

@@ -0,0 +1,18 @@
+use serde_json::{Map, Value};
+
+use crate::{
+    GeminiVideoTaskSeed, LocalVideoTaskReadResponse, LocalVideoTaskRegistryMutation,
+    LocalVideoTaskSnapshot, OpenAiVideoTaskSeed,
+};
+
+pub trait VideoTaskStore: std::fmt::Debug + Send + Sync {
+    fn insert(&self, snapshot: LocalVideoTaskSnapshot);
+    fn read_openai(&self, task_id: &str) -> Option<LocalVideoTaskReadResponse>;
+    fn read_gemini(&self, short_id: &str) -> Option<LocalVideoTaskReadResponse>;
+    fn clone_openai(&self, task_id: &str) -> Option<OpenAiVideoTaskSeed>;
+    fn clone_gemini(&self, short_id: &str) -> Option<GeminiVideoTaskSeed>;
+    fn list_active_snapshots(&self, limit: usize) -> Vec<LocalVideoTaskSnapshot>;
+    fn apply_mutation(&self, mutation: LocalVideoTaskRegistryMutation);
+    fn project_openai(&self, task_id: &str, provider_body: &Map<String, Value>) -> bool;
+    fn project_gemini(&self, short_id: &str, provider_body: &Map<String, Value>) -> bool;
+}