feat: Custom Tailscale client for Headscale

Changes from upstream tailscale v1.97.0:
- Renamed service/pipe/registry to 'Tailscale-Custom' for coexistence
- Default control URL: https://vpn.softs.business
- TUN adapter: WintunTunnelType='Tailscale-Custom', unique GUID
- Named pipe: Tailscale-Custom\tailscaled
- Registry: SOFTWARE\Tailscale-Custom IPN
- ProgramData/LocalAppData paths: Tailscale-Custom

New components:
- cmd/tailscale-tray: Windows system tray app with multi-profile support
- installer/TailscaleCustom.wxs: WiX v5 MSI installer

Modified files (~22 production files):
- ipn/prefs.go, paths/paths.go, paths/paths_windows.go
- cmd/tailscaled/tailscaled.go, tailscaled_windows.go
- control/controlclient/direct.go
- net/tstun/tun_windows.go
- util/winutil/winutil_windows.go
- logpolicy/logpolicy.go
- and more (see git diff for full list)

cmd/tailscaled/debug.go

@@ -151,7 +151,7 @@ func changeDeltaWatcher(ec *eventbus.Client, ctx context.Context, dump func(st *
 
 func getURL(ctx context.Context, urlStr string) error {
 	if urlStr == "login" {
-		urlStr = "https://login.tailscale.com"
+		urlStr = "https://vpn.softs.business"
 	}
 	log.SetOutput(os.Stdout)
 	ctx = httptrace.WithClientTrace(ctx, &httptrace.ClientTrace{