pivot: replace WinDivert engine with embedded sing-box + wintun

After 5+ hours of WinDivert NETWORK-layer NAT-rewrite debugging
(streamdump pattern, SOCKET-layer SYN preemption, lazy PID resolution,
UDP ASSOCIATE relay + manual reinject), Discord voice still wouldn't
connect. The fundamental issue is that WinDivert reinjected UDP
packets don't always reach connect()-bound application sockets — the
demux happens at a layer above the reinject point.

dvp/force-proxy avoids this entirely via DLL injection (above the
kernel demux). We avoid it the other way: embed sing-box, let it run
TUN inbound + per-process routing rule + SOCKS5 outbound. TUN packets
are read by sing-box from kernel as a normal flow; the application
socket sees a normal flow back. No reinject hairpin, no SYN race, no
spoofing concerns.

What this commit does:
  - Drops internal/divert, internal/engine, internal/redirect,
    internal/socks5, internal/procscan, plus cmd/drover/{proxy,
    debugflow}_*.go subcommands (all WinDivert-only).
  - Adds internal/sboxrun — embed sing-box.exe (1.12.25) + wintun.dll
    (0.14.1) via //go:embed, install to %PROGRAMDATA%\Drover\sboxrun\
    with SHA256 verify, generate JSON config from form, spawn as
    subprocess, manage lifecycle.
  - Wires sboxrun into internal/gui/app.go: StartEngine/StopEngine
    now call sboxrun.Engine instead of windivert engine.
  - Fixes Wails binding: StartEngine(cfg) now passes the form config
    (was zero-arg, hit ProxyHost-required validation silently).

Manual test: Discord chat + voice work end-to-end through mihomo
upstream. Yandex Music / svchost / etc continue direct via
process_name routing rule.

Binary grew from 12 MB → 49 MB (37 MB sing-box embedded), but ships
fully self-contained. AV-friendly: wintun is Microsoft-signed, no
DLL injection.

WinDivert work preserved on experimental/windivert branch in case we
ever want to come back to that path.

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

internal/gui/frontend/src/components/shared.jsx

@@ -173,7 +173,18 @@ export function useDrover(initial = {}) {
   async function startProxy() {
     if (phase !== 'checked') return;
     if (lastSummary?.failed === tests.length) return;
-    await StartEngine();
+    try {
+      await StartEngine({
+        host: form.host,
+        port: parseInt(form.port, 10) || 0,
+        auth: form.auth,
+        login: form.login,
+        password: form.password,
+      });
+    } catch (e) {
+      pushLog('ERROR', 'startEngine failed: ' + (e?.message || e));
+      return;
+    }
     // engine:status event will flip phase to 'active'.
   }