feat: SDWAN data plane + UDP punch port fix + TUN reader

SDWAN:
- protocol: add SDWANConfig/SDWANPeer/SDWANPacket structs, MsgTunnel type
- server: sdwan.go (JSON file store), sdwan_api.go (Get/Set/broadcast/route)
- server: push SDWAN config on login, announce peer online/offline events
- server: RouteSDWANPacket routes TUN packets between nodes via signaling
- client: TUN device setup (optun), tunReadLoop reads IP packets
- client: handle SDWANConfig/SDWANPeer/SDWANDel push messages
- client: apply routes (per-node /32 + broad CIDR fallback)

UDP punch fix:
- nat/detect: capture LocalPort from STUN UDP socket for punch binding
- client: pass publicPort + localPort through login and punch config
- coordinator: include PublicPort in PunchParams for both sides
- protocol: add PublicPort to LoginReq and ReportBasic

Other:
- server: use client-reported PublicIP instead of raw r.RemoteAddr
- server: update PublicIP/Port from ReportBasic if provided
- client: config file loading with zero-value defaults backfill
- .gitignore: exclude run/, *.pid, *.log, sdwan.json
- go.mod: add golang.org/x/sys for TUN ioctl

cmd/inp2pc/main.go

@@ -51,6 +51,34 @@ func main() {
 			var fileCfg config.ClientConfig
 			if err := json.Unmarshal(data, &fileCfg); err == nil {
 				cfg = fileCfg
+				// fill defaults for missing fields
+				if cfg.ServerPort == 0 {
+					cfg.ServerPort = config.DefaultWSPort
+				}
+				if cfg.STUNUDP1 == 0 {
+					cfg.STUNUDP1 = config.DefaultSTUNUDP1
+				}
+				if cfg.STUNUDP2 == 0 {
+					cfg.STUNUDP2 = config.DefaultSTUNUDP2
+				}
+				if cfg.STUNTCP1 == 0 {
+					cfg.STUNTCP1 = config.DefaultSTUNTCP1
+				}
+				if cfg.STUNTCP2 == 0 {
+					cfg.STUNTCP2 = config.DefaultSTUNTCP2
+				}
+				if cfg.RelayPort == 0 {
+					cfg.RelayPort = config.DefaultRelayPort
+				}
+				if cfg.MaxRelayLoad == 0 {
+					cfg.MaxRelayLoad = config.DefaultMaxRelayLoad
+				}
+				if cfg.ShareBandwidth == 0 {
+					cfg.ShareBandwidth = 10
+				}
+				if cfg.LogLevel == 0 {
+					cfg.LogLevel = 1
+				}
 				log.Printf("[main] loaded config from %s", *configFile)
 			}
 		}