新增: 跨端WS隧道脚手架(df-tunnel客户端+df-relay云中继)

df-tunnel:桌面端出站WS客户端(TunnelClient trait+骨架,穿NAT连云后端)
df-relay:axum WS中继服务(转发小程序↔桌面端,广播骨架)
双crate独立消息骨架,不依赖src-tauri/df-types避跨crate强耦合
workspace crates/* glob自动注册,Phase2填充WS握手/鉴权/重连/路由

crates/df-relay/Cargo.toml

@@ -0,0 +1,19 @@
+[package]
+name = "df-relay"
+version = "0.1.0"
+edition = "2021"
+description = "跨端 AI Chat 云中继服务(axum WS Server,转发小程序 ↔ 桌面端)"
+
+[dependencies]
+serde = { workspace = true }
+serde_json = { workspace = true }
+tokio = { workspace = true }
+async-trait = { workspace = true }
+thiserror = { workspace = true }
+anyhow = { workspace = true }
+tracing = { workspace = true }
+
+# HTTP + WS 服务端
+axum = { version = "0.7", features = ["ws"] }
+tokio-tungstenite = { version = "0.23", features = ["native-tls"] }
+futures-util = "0.3"