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/constants.rs

@@ -9,6 +9,9 @@ pub(crate) const FORWARDED_PROTO_HEADER: &str = "x-forwarded-proto";
 pub(crate) const GATEWAY_HEADER: &str = "x-aether-gateway";
 pub(crate) const EXECUTION_PATH_HEADER: &str = "x-aether-execution-path";
 pub(crate) const DEPENDENCY_REASON_HEADER: &str = "x-aether-dependency-reason";
+pub(crate) const EXECUTION_RUNTIME_LOOP_GUARD_HEADER: &str = "x-aether-execution-loop-guard";
+pub(crate) const EXECUTION_RUNTIME_LOOP_GUARD_VALUE: &str = "local-runtime";
+pub(crate) const EXECUTION_RUNTIME_LOOP_GUARD_VIA_TOKEN: &str = "aether-execution-runtime";
 pub(crate) const LOCAL_EXECUTION_RUNTIME_MISS_REASON_HEADER: &str =
     "x-aether-local-execution-runtime-miss-reason";
 pub(crate) const TUNNEL_AFFINITY_FORWARDED_BY_HEADER: &str =
@@ -29,6 +32,8 @@ pub(crate) const EXECUTION_PATH_LOCAL_ROUTE_NOT_FOUND: &str = "local_route_not_f
 pub(crate) const EXECUTION_PATH_LOCAL_OVERLOADED: &str = "local_overloaded";
 pub(crate) const EXECUTION_PATH_DISTRIBUTED_OVERLOADED: &str = "distributed_overloaded";
 pub(crate) const EXECUTION_PATH_LOCAL_AI_PUBLIC: &str = "local_ai_public";
+pub(crate) const EXECUTION_PATH_LOCAL_EXECUTION_LOOP_DETECTED: &str =
+    "local_execution_loop_detected";
 pub(crate) const CONTROL_ROUTE_CLASS_HEADER: &str = "x-aether-control-route-class";
 pub(crate) const CONTROL_ROUTE_FAMILY_HEADER: &str = "x-aether-control-route-family";
 pub(crate) const CONTROL_ROUTE_KIND_HEADER: &str = "x-aether-control-route-kind";