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)

paths/paths.go

@@ -23,7 +23,7 @@ var AppSharedDir syncs.AtomicValue[string]
 // or the empty string if there's no reasonable default.
 func DefaultTailscaledSocket() string {
 	if runtime.GOOS == "windows" {
-		return `\\.\pipe\ProtectedPrefix\Administrators\Tailscale\tailscaled`
+		return `\\.\pipe\ProtectedPrefix\Administrators\Tailscale-Custom\tailscaled`
 	}
 	if runtime.GOOS == "darwin" {
 		return "/var/run/tailscaled.socket"
@@ -66,7 +66,7 @@ func DefaultTailscaledStateFile() string {
 		return f()
 	}
 	if runtime.GOOS == "windows" {
-		return filepath.Join(os.Getenv("ProgramData"), "Tailscale", "server-state.conf")
+		return filepath.Join(os.Getenv("ProgramData"), "Tailscale-Custom", "server-state.conf")
 	}
 	return ""
 }
@@ -118,7 +118,7 @@ func MkStateDir(dirPath string) error {
 // It is only called on Windows.
 func LegacyStateFilePath() string {
 	if runtime.GOOS == "windows" {
-		return filepath.Join(os.Getenv("LocalAppData"), "Tailscale", "server-state.conf")
+		return filepath.Join(os.Getenv("LocalAppData"), "Tailscale-Custom", "server-state.conf")
 	}
 	return ""
 }

paths/paths_windows.go

@@ -38,7 +38,7 @@ func ensureStateDirPermsWindows(dirPath string) error {
 	if !fi.IsDir() {
 		return os.ErrInvalid
 	}
-	if strings.ToLower(filepath.Base(dirPath)) != "tailscale" {
+	if strings.ToLower(filepath.Base(dirPath)) != "tailscale-custom" {
 		return nil
 	}