cmd/drover: UAC re-launch helper for non-admin invocations

CLI subcommands (check/version/update) don't need driver access and
run as user. Bare drover.exe (GUI/engine mode) requires admin for
WinDivertOpen — re-launches via ShellExecute("runas") and exits.

Per spec decision B1: prompt at every launch, no scheduled-task
trampoline.

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

cmd/drover/main.go

@@ -29,6 +29,17 @@ func main() {
 	// AttachConsole(ATTACH_PARENT_PROCESS) wires that up. No-op elsewhere.
 	attachToParentConsole()
 
+	// Detect if we need admin for the command in os.Args[1:]. If we do and
+	// we're not admin, re-launch via ShellExecute("runas", ...) and exit.
+	// CLI subcommands like "check", "version", "update" don't need admin
+	// and will run without UAC prompt.
+	if CmdNeedsAdmin(os.Args[1:]) && !IsAdmin() {
+		if err := ReElevate(os.Args[1:]); err != nil {
+			fmt.Fprintf(os.Stderr, "failed to re-elevate: %v\n", err)
+		}
+		os.Exit(0)
+	}
+
 	// Inject our build version so the updater package can stamp it on the
 	// User-Agent header it sends to git.okcu.io.
 	updater.SetVersion(Version)