experimental/windivert: P2.1+P2.2 with WinDivert NETWORK+SOCKET layers

WIP snapshot before pivot to sing-box+TUN. Reached:
- TCP redirect via streamdump pattern (swap+Outbound=0+reinject)
- SOCKET layer for SYN-stage flow detection (avoids FLOW Establish-too-late race)
- Lazy PID→name resolution (catches Update.exe inside procscan tick)
- UDP forward via SOCKS5 UDP ASSOCIATE relay + manual reinject
- Result: chat works, voice times out (Discord IP discovery / RTC handshake fails)

Reason for pivot: WinDivert NAT-reinject pattern has subtle layer-3
semantics issues that DLL-injection / TUN-based proxies sidestep
entirely. Going with embedded sing-box + wintun as the engine —
proven path for Discord voice through SOCKS5.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

internal/gui/app.go

@@ -6,6 +6,7 @@ package gui
 import (
 	"context"
 	"fmt"
+	"log"
 	"math/rand"
 	"sync"
 	"time"
@@ -175,9 +176,11 @@ func (a *App) CancelCheck() {
 
 // StartEngine initializes and brings up the engine with the given config.
 func (a *App) StartEngine(cfg Config) error {
+	log.Printf("gui: StartEngine called host=%s port=%d auth=%v", cfg.Host, cfg.Port, cfg.Auth)
 	a.mu.Lock()
 	defer a.mu.Unlock()
 	if a.eng != nil && a.eng.Status() == engine.StatusActive {
+		log.Printf("gui: StartEngine no-op (already active)")
 		return nil
 	}
 	e, err := engine.New(engine.Config{
@@ -188,15 +191,18 @@ func (a *App) StartEngine(cfg Config) error {
 		Targets:   []string{"Discord.exe", "DiscordCanary.exe", "DiscordPTB.exe", "Update.exe"},
 	})
 	if err != nil {
+		log.Printf("gui: engine.New failed: %v", err)
 		runtime.EventsEmit(a.ctx, "engine:status", map[string]any{"running": false, "error": err.Error()})
 		return err
 	}
 	if err := e.Start(a.ctx); err != nil {
+		log.Printf("gui: engine.Start failed: %v", err)
 		runtime.EventsEmit(a.ctx, "engine:status", map[string]any{"running": false, "error": err.Error()})
 		return err
 	}
 	a.eng = e
 	a.startedAt = time.Now()
+	log.Printf("gui: engine started, status=%s", e.Status())
 	runtime.EventsEmit(a.ctx, "engine:status", map[string]any{"running": true})
 	return nil
 }