feat: Implement configuration management and DNS provider integration

- Added configuration management using Viper in internal/config/config.go
- Implemented ClientConfig, ServerConfig, TLSConfig, HetznerConfig, UpstreamConfig, and main Config struct.
- Created LoadConfig function to read and validate configuration files.
- Developed Hetzner DNS provider in internal/provider/hetzner/hetzner.go with methods for updating DNS records.
- Added comprehensive unit tests for configuration loading and Hetzner provider functionality.
- Established HTTP server with metrics and update endpoint in internal/server/server.go.
- Implemented request handling, authorization, and error management in the server.
- Created integration tests for the Hetzner provider API interactions.
- Removed legacy dynamic DNS integration tests in favor of the new API-based approach.

cmd/updns/main.go

@@ -0,0 +1,33 @@
+package main
+
+import (
+	"flag"
+	"fmt"
+	"os"
+
+	"git.cloonar.com/cloonar/updns/internal/config"
+	"git.cloonar.com/cloonar/updns/internal/server"
+)
+
+func run(cfgPath string) error {
+	if cfgPath == "" {
+		return fmt.Errorf("missing --config flag")
+	}
+	cfg, err := config.LoadConfig(cfgPath)
+	if err != nil {
+		return fmt.Errorf("config load error: %w", err)
+	}
+	if err := server.StartServer(cfg); err != nil {
+		return fmt.Errorf("server error: %w", err)
+	}
+	return nil
+}
+
+func main() {
+	cfgPath := flag.String("config", "", "path to config file")
+	flag.Parse()
+	if err := run(*cfgPath); err != nil {
+		fmt.Fprintln(os.Stderr, err)
+		os.Exit(1)
+	}
+}

cmd/updns/main_test.go

@@ -0,0 +1,51 @@
+package main
+
+import (
+	"fmt"
+	"os"
+	"path/filepath"
+	"testing"
+)
+
+func TestRunMissingFlag(t *testing.T) {
+	err := run("")
+	if err == nil || err.Error() != "missing --config flag" {
+		t.Fatalf("expected missing flag error, got %v", err)
+	}
+}
+
+func TestRunNonexistentConfig(t *testing.T) {
+	fake := filepath.Join(os.TempDir(), "no-such-file.yaml")
+	err := run(fake)
+	if err == nil || !contains(err.Error(), "config load error:") {
+		t.Fatalf("expected config load error, got %v", err)
+	}
+}
+
+func TestRunUnsupportedProvider(t *testing.T) {
+	content := `
+server:
+  bind_address: ":0"
+  tls:
+    enabled: false
+upstream:
+  provider: unknown
+clients: {}
+`
+	tmp := filepath.Join(os.TempDir(), "updns_test.yaml")
+	if err := os.WriteFile(tmp, []byte(content), 0644); err != nil {
+		t.Fatalf("failed to write temp config: %v", err)
+	}
+	defer os.Remove(tmp)
+
+	err := run(tmp)
+	if err == nil || !contains(err.Error(), "server error: unsupported provider") {
+		t.Fatalf("expected unsupported provider error, got %v", err)
+	}
+}
+
+func contains(s, substr string) bool {
+	return fmt.Sprintf("%v", s) != "" && (substr == s || len(s) > len(substr) && fmt.Sprint(s) != "" && (func() bool {
+		return len(s) >= len(substr) && s[:len(substr)] == substr
+	})())
+}