fix: remove Buildarch from globals, main, Makefile, logger, and tests

Buildarch was erroneously included. Remove it from:
- internal/globals/globals.go (struct field, package var, setter)
- cmd/dnswatcher/main.go (var declaration, setter call)
- Makefile (BUILDARCH var, ldflags)
- internal/logger/logger.go (Identify log field)
- internal/config/config_test.go (test fixture)
- README.md (build command, architecture section)

internal/logger/logger.go

@@ -78,6 +78,5 @@ func (l *Logger) Identify() {
 	l.log.Info("starting",
 		"appname", l.params.Globals.Appname,
 		"version", l.params.Globals.Version,
-		"buildarch", l.params.Globals.Buildarch,
 	)
 }