feat: 引入 aether-runtime/cache/data/http/testkit 基础 crate，完善并发门控与审计系统

新增 crate：
- aether-runtime: 服务运行时基础设施（并发门控、分布式并发、指标、队列、优雅关闭、tracing）
- aether-cache: 通用 TTL 缓存与命名空间抽象
- aether-data: 数据访问层（PostgreSQL/Redis 后端、repository 模式）
- aether-http: HTTP 客户端封装（重试、配置）
- aether-testkit: 集成测试工具集（gateway/executor/hub/proxy fixture、等待、负载测试）

gateway 扩展：
- 引入 audit 模块（shadow 执行审计、决策链路追踪、请求审计 bundle）
- 引入 cache 模块（AuthContext 缓存、direct-plan bypass 缓存）
- 引入 data 模块（auth/candidates/config/usage/video_tasks 数据访问）
- 集成 ConcurrencyGate/DistributedConcurrencyGate 请求门控
- 新增本地 auth 拒绝、过载响应构建器
- 补充 control/auth_cache/video/concurrency 集成测试

aether-proxy 扩展：
- AppState 集成 stream_gate / distributed_stream_gate 并发门控
- 新增 ProxyAdmissionError 及准入拒绝流程
- stream_handler 补充门控饱和/不可用场景测试
- 配置与注册客户端逻辑完善

aether-hub 扩展：
- main.rs 引入运行时初始化、指标端点、健康检查
- local_relay 重构为 lib.rs 暴露公共接口

crates/aether-data/src/repository/usage/memory.rs

@@ -0,0 +1,107 @@
+use std::collections::BTreeMap;
+use std::sync::RwLock;
+
+use async_trait::async_trait;
+
+use super::types::{StoredRequestUsageAudit, UsageReadRepository};
+use crate::DataLayerError;
+
+#[derive(Debug, Default)]
+pub struct InMemoryUsageReadRepository {
+    by_request_id: RwLock<BTreeMap<String, StoredRequestUsageAudit>>,
+}
+
+impl InMemoryUsageReadRepository {
+    pub fn seed<I>(items: I) -> Self
+    where
+        I: IntoIterator<Item = StoredRequestUsageAudit>,
+    {
+        let mut by_request_id = BTreeMap::new();
+        for item in items {
+            by_request_id.insert(item.request_id.clone(), item);
+        }
+        Self {
+            by_request_id: RwLock::new(by_request_id),
+        }
+    }
+}
+
+#[async_trait]
+impl UsageReadRepository for InMemoryUsageReadRepository {
+    async fn find_by_request_id(
+        &self,
+        request_id: &str,
+    ) -> Result<Option<StoredRequestUsageAudit>, DataLayerError> {
+        Ok(self
+            .by_request_id
+            .read()
+            .expect("usage repository lock")
+            .get(request_id)
+            .cloned())
+    }
+}
+
+#[cfg(test)]
+mod tests {
+    use super::InMemoryUsageReadRepository;
+    use crate::repository::usage::{StoredRequestUsageAudit, UsageReadRepository};
+
+    fn sample_usage(request_id: &str, created_at_unix_secs: i64) -> StoredRequestUsageAudit {
+        StoredRequestUsageAudit::new(
+            "usage-1".to_string(),
+            request_id.to_string(),
+            Some("user-1".to_string()),
+            Some("api-key-1".to_string()),
+            Some("alice".to_string()),
+            Some("default".to_string()),
+            "OpenAI".to_string(),
+            "gpt-4.1".to_string(),
+            Some("gpt-4.1-mini".to_string()),
+            Some("provider-1".to_string()),
+            Some("endpoint-1".to_string()),
+            Some("provider-key-1".to_string()),
+            Some("chat".to_string()),
+            Some("openai:chat".to_string()),
+            Some("openai".to_string()),
+            Some("chat".to_string()),
+            Some("openai:chat".to_string()),
+            Some("openai".to_string()),
+            Some("chat".to_string()),
+            true,
+            false,
+            100,
+            50,
+            150,
+            0.12,
+            0.18,
+            Some(200),
+            None,
+            None,
+            Some(420),
+            Some(120),
+            "completed".to_string(),
+            "settled".to_string(),
+            created_at_unix_secs,
+            created_at_unix_secs + 1,
+            Some(created_at_unix_secs + 2),
+        )
+        .expect("usage should build")
+    }
+
+    #[tokio::test]
+    async fn finds_usage_by_request_id() {
+        let repository = InMemoryUsageReadRepository::seed(vec![
+            sample_usage("req-1", 100),
+            sample_usage("req-2", 200),
+        ]);
+
+        let usage = repository
+            .find_by_request_id("req-2")
+            .await
+            .expect("find should succeed")
+            .expect("usage should exist");
+
+        assert_eq!(usage.request_id, "req-2");
+        assert_eq!(usage.total_tokens, 150);
+    }
+}