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)

Makefile

@@ -2,8 +2,7 @@
 
 BINARY := dnswatcher
 VERSION := $(shell git describe --tags --always --dirty 2>/dev/null || echo "dev")
-BUILDARCH := $(shell go env GOARCH)
-LDFLAGS := -X main.Version=$(VERSION) -X main.Buildarch=$(BUILDARCH)
+LDFLAGS := -X main.Version=$(VERSION)
 
 all: check build