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。

apps/aether-gateway/src/cache/auth_api_key_last_used.rs

@@ -0,0 +1,19 @@
+use std::time::Duration;
+
+use aether_cache::ExpiringMap;
+
+#[derive(Debug, Default)]
+pub(crate) struct AuthApiKeyLastUsedCache {
+    entries: ExpiringMap<String, ()>,
+}
+
+impl AuthApiKeyLastUsedCache {
+    pub(crate) fn should_touch(&self, api_key_id: &str, ttl: Duration, max_entries: usize) -> bool {
+        let key = api_key_id.to_string();
+        if self.entries.contains_fresh(&key, ttl) {
+            return false;
+        }
+        self.entries.insert(key, (), ttl, max_entries);
+        true
+    }
+}

apps/aether-gateway/src/cache/auth_context.rs

@@ -0,0 +1,31 @@
+use std::time::Duration;
+
+use aether_cache::ExpiringMap;
+
+use crate::control::GatewayControlAuthContext;
+
+#[derive(Debug, Default)]
+pub(crate) struct AuthContextCache {
+    entries: ExpiringMap<String, GatewayControlAuthContext>,
+}
+
+impl AuthContextCache {
+    pub(crate) fn get_fresh(
+        &self,
+        cache_key: &str,
+        ttl: Duration,
+    ) -> Option<GatewayControlAuthContext> {
+        self.entries.get_fresh(&cache_key.to_string(), ttl)
+    }
+
+    pub(crate) fn insert(
+        &self,
+        cache_key: String,
+        auth_context: GatewayControlAuthContext,
+        ttl: Duration,
+        max_entries: usize,
+    ) {
+        self.entries
+            .insert(cache_key, auth_context, ttl, max_entries);
+    }
+}

apps/aether-gateway/src/cache/direct_plan_bypass.rs

@@ -0,0 +1,18 @@
+use std::time::Duration;
+
+use aether_cache::ExpiringMap;
+
+#[derive(Debug, Default)]
+pub(crate) struct DirectPlanBypassCache {
+    entries: ExpiringMap<String, ()>,
+}
+
+impl DirectPlanBypassCache {
+    pub(crate) fn should_skip(&self, cache_key: &str, ttl: Duration) -> bool {
+        self.entries.contains_fresh(&cache_key.to_string(), ttl)
+    }
+
+    pub(crate) fn mark(&self, cache_key: String, ttl: Duration, max_entries: usize) {
+        self.entries.insert(cache_key, (), ttl, max_entries);
+    }
+}

apps/aether-gateway/src/cache/mod.rs

@@ -0,0 +1,9 @@
+mod auth_api_key_last_used;
+mod auth_context;
+mod direct_plan_bypass;
+mod scheduler_affinity;
+
+pub(crate) use auth_api_key_last_used::AuthApiKeyLastUsedCache;
+pub(crate) use auth_context::AuthContextCache;
+pub(crate) use direct_plan_bypass::DirectPlanBypassCache;
+pub(crate) use scheduler_affinity::{SchedulerAffinityCache, SchedulerAffinityTarget};

apps/aether-gateway/src/cache/scheduler_affinity.rs

@@ -0,0 +1,34 @@
+use std::time::Duration;
+
+use aether_cache::ExpiringMap;
+pub(crate) use aether_scheduler_core::SchedulerAffinityTarget;
+
+#[derive(Debug, Default)]
+pub(crate) struct SchedulerAffinityCache {
+    entries: ExpiringMap<String, SchedulerAffinityTarget>,
+}
+
+impl SchedulerAffinityCache {
+    pub(crate) fn get_fresh(
+        &self,
+        cache_key: &str,
+        ttl: Duration,
+    ) -> Option<SchedulerAffinityTarget> {
+        self.entries.get_fresh(&cache_key.to_string(), ttl)
+    }
+
+    #[cfg_attr(not(test), allow(dead_code))]
+    pub(crate) fn insert(
+        &self,
+        cache_key: String,
+        target: SchedulerAffinityTarget,
+        ttl: Duration,
+        max_entries: usize,
+    ) {
+        self.entries.insert(cache_key, target, ttl, max_entries);
+    }
+
+    pub(crate) fn remove(&self, cache_key: &str) -> Option<SchedulerAffinityTarget> {
+        self.entries.remove(&cache_key.to_string())
+    }
+}