feat(aether-proxy): 网络层全面优化与代理耗时追踪

aether-proxy:
- 新增 20+ 可配置参数：Aether API/delegate/CONNECT 各阶段超时、连接池、TCP keepalive/nodelay
- AetherClient 支持指数退避重试(可配置次数/延迟)和 HTTP/2
- 新增 DNS 缓存(TTL + 容量限制)避免重复解析
- 新增并发连接数限制(Semaphore，默认基于硬件估算)
- CONNECT 隧道增加建连超时和升级超时
- TLS 增加握手超时、会话缓存(session ticket + memory cache)、ALPN 协商
- 新增 ProxyMetrics 收集请求计数和延迟，通过心跳上报
- delegate 响应注入 X-Proxy-Timing 头(dns_ms/upstream_ms/total_ms)

后端:
- StreamContext 和 handler 提取 X-Proxy-Timing 写入 proxy_info 追踪数据

前端:
- 请求时间线展示代理分阶段耗时(DNS/上游)
- Endpoint 添加按钮改为文字按钮样式

aether-proxy/src/setup/tui.rs

@@ -209,6 +209,26 @@ impl App {
             heartbeat_interval: None,
             allowed_ports: None,
             timestamp_tolerance: None,
+            aether_request_timeout_secs: None,
+            aether_connect_timeout_secs: None,
+            aether_pool_max_idle_per_host: None,
+            aether_pool_idle_timeout_secs: None,
+            aether_tcp_keepalive_secs: None,
+            aether_tcp_nodelay: None,
+            aether_http2: None,
+            aether_retry_max_attempts: None,
+            aether_retry_base_delay_ms: None,
+            aether_retry_max_delay_ms: None,
+            max_concurrent_connections: None,
+            connect_timeout_secs: None,
+            tls_handshake_timeout_secs: None,
+            dns_cache_ttl_secs: None,
+            dns_cache_capacity: None,
+            delegate_connect_timeout_secs: None,
+            delegate_pool_max_idle_per_host: None,
+            delegate_pool_idle_timeout_secs: None,
+            delegate_tcp_keepalive_secs: None,
+            delegate_tcp_nodelay: None,
             log_level: get("log_level"),
             log_json: get("log_json").and_then(|v| v.parse().ok()),
             enable_tls: None,