sboxrun: domain+IP-CIDR rules + remove voice-quality test

Three follow-up fixes after the WinDivert→sing-box pivot:

1. Discord updater now routes through upstream. Previously only the
   process-name rule matched, but sing-box's TUN-side process
   detection on Windows mis-attributes the in-process Rust updater's
   TLS connection to e.g. steam.exe — the connection went direct and
   hit RKN block. Adding domain_suffix + ip_cidr rules for Cloudflare
   (162.159/16, 104.16/13, 172.64/13) and Fastly (199.232/16,
   151.101/16) catches updates.discord.com regardless of which PID
   the kernel claims sent it. Verified via curl through mihomo:
   updates.discord.com responds 400 in 393ms (i.e. TLS handshake
   succeeds, only the path is wrong — proves the routing reaches it).

2. DiscordSystemHelper.exe added to TargetProcs alongside Update.exe
   (modern Discord builds use it for elevated updates).

3. UDP voice quality test removed from the checker. The STUN-via-
   relay burst measured private mihomo BND.ADDR (192.168.1.132)
   which is unroutable from external clients, so the test reported
   100% loss every time despite voice actually working through
   sing-box's TUN+SOCKS5. The remaining 6 checks (TCP/greet/auth/
   connect/UDP/api) cover what's actionable; voice quality is
   verified empirically by joining a Discord call.

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

internal/gui/app.go

@@ -189,7 +189,13 @@ func (a *App) StartEngine(cfg Config) error {
 		UseAuth:     cfg.Auth,
 		Login:       cfg.Login,
 		Password:    cfg.Password,
-		TargetProcs: []string{"Discord.exe", "DiscordCanary.exe", "DiscordPTB.exe", "Update.exe"},
+		TargetProcs: []string{
+			"Discord.exe",
+			"DiscordCanary.exe",
+			"DiscordPTB.exe",
+			"DiscordSystemHelper.exe", // elevated updater (modern builds)
+			"Update.exe",              // legacy Squirrel updater (older builds)
+		},
 	})
 	if err != nil {
 		log.Printf("gui: sboxrun.New failed: %v", err)