feat: 新增 frontdoor 执行回环守卫与多项可观测性增强

- 新增 frontdoor_loop_guard 模块，检测并拒绝 execution runtime 回环到本地网关的请求（HTTP 508）
- candidate loop 引入 span tracking、执行尝试日志与流式看门狗超时
- 本地故障转移策略支持从 report_context 加载，新增 append_local_failover_policy_to_value
- runtime tracing 美化：移除 identity 前缀，按 span 深度树形缩进，target 固定宽度展示
- Codex OpenAI CLI 补齐 chatgpt-account-id/x-client-request-id/session_id/conversation_id 请求头
- OpenAI CLI same/cross-format 聚合规则放宽以支持 openai:compact 客户端格式，并过滤 error-like 响应体
- auth/proxy/finalize 日志补充 user_id/api_key_id/api_key_name/balance_remaining 等字段
- 启动日志拆分为 starting/ready/config 三段，新增 resolve_bind_http_base_url
- access_log middleware 将生成的 trace_id 回注到下游请求头
- Cargo.toml 启用 serde_json preserve_order 特性

apps/aether-gateway/src/lib.rs

@@ -40,6 +40,7 @@ mod error;
 mod execution_runtime;
 mod executor;
 mod fallback_metrics;
+mod frontdoor_loop_guard;
 mod handlers;
 mod headers;
 mod hooks;
@@ -68,7 +69,8 @@ pub use self::async_task::VideoTaskTruthSourceMode;
 pub use self::data::GatewayDataConfig;
 pub(crate) use self::error::GatewayError;
 pub(crate) use self::execution_runtime::{
-    append_execution_contract_fields_to_value, MAX_ERROR_BODY_BYTES, MAX_STREAM_PREFETCH_FRAMES,
+    append_execution_contract_fields_to_value, append_local_failover_policy_to_value,
+    MAX_ERROR_BODY_BYTES, MAX_STREAM_PREFETCH_FRAMES,
 };
 pub use self::execution_runtime::{
     build_execution_runtime_router, build_execution_runtime_router_with_request_concurrency_limit,