fix: SDWAN TUN device lifecycle + stability

Key fixes:
- SDWAN config: use absolute path /root/.openclaw/workspace/inp2p/sdwan.json
- Client: register handlers BEFORE ReadLoop (race condition fix)
- Client: make ensureTUNReader non-fatal on error
- Client: fix TUN device conflict between ip tuntap add and ioctl
- Client: fix panic on empty TUN read (n==0 check)
- Build: static binary with -extldflags=-static for glibc compatibility

Verified: hcss(10.10.0.3) <-> i-6986(10.10.0.2) ping 5/5, 0% loss, 44ms

internal/server/sdwan_api.go

@@ -1,6 +1,7 @@
 package server
 
 import (
+	"log"
 	"net/netip"
 
 	"github.com/openp2p-cn/inp2p/pkg/protocol"
@@ -107,6 +108,7 @@ func (s *Server) announceSDWANNodeOffline(nodeName string) {
 }
 
 func (s *Server) RouteSDWANPacket(from *NodeInfo, pkt protocol.SDWANPacket) {
+	log.Printf("[sdwan] route: %s -> %s len=%d", from.Name, pkt.DstIP, len(pkt.Payload))
 	if from == nil {
 		return
 	}