add initial Go implementation of arcline-audit

Implements the full site health auditor with four check groups:

  - SSL/TLS (certificate validity, expiry, chain, TLS version, ciphers)

  - HTTP (redirect chain, security headers, response time)

  - DNS (A/AAAA, MX, SPF, DKIM, DMARC, DNSSEC)

  - Infrastructure (CDN detection, common port probes)

Includes CLI with --checks filter, --json and --out flags,

cross-compile Makefile, and GitLab CI pipeline.

Signed-off-by: Blake Ridgway <blake@blakeridgway.com>

Makefile

@@ -0,0 +1,31 @@
+.PHONY: build clean test lint linux darwin windows all release
+
+BINARY := arcline-audit
+LDFLAGS := -s -w
+MAIN := ./cmd/arcline-audit
+
+build:
+	CGO_ENABLED=0 go build -trimpath -ldflags "$(LDFLAGS)" -o $(BINARY) $(MAIN)
+
+clean:
+	rm -f $(BINARY) arcline-audit-*
+
+test:
+	go test ./...
+
+lint:
+	go vet ./...
+
+# Cross-compile targets
+linux:
+	GOOS=linux GOARCH=amd64 CGO_ENABLED=0 go build -trimpath -ldflags "$(LDFLAGS)" -o $(BINARY)-linux-amd64 $(MAIN)
+
+darwin:
+	GOOS=darwin GOARCH=amd64 CGO_ENABLED=0 go build -trimpath -ldflags "$(LDFLAGS)" -o $(BINARY)-darwin-amd64 $(MAIN)
+
+windows:
+	GOOS=windows GOARCH=amd64 CGO_ENABLED=0 go build -trimpath -ldflags "$(LDFLAGS)" -o $(BINARY)-windows-amd64.exe $(MAIN)
+
+# Release builds for all platforms
+release: linux darwin windows
+