feat: add cloud-init Go parser (Phase 2)

Implement a lightweight cloud-init system for first-boot configuration:
- Go parser for YAML config (hostname, network, KubeSolo settings)
- Static/DHCP network modes with DNS override
- KubeSolo extra flags and API server SAN configuration
- Portainer Edge Agent and air-gapped deployment support
- New init stage 45-cloud-init.sh runs before network/hostname stages
- Stages 50/60 skip gracefully when cloud-init has already applied
- Build script compiles static Linux/amd64 binary (~2.7 MB)
- 17 unit tests covering parsing, validation, and example files
- Full documentation at docs/cloud-init.md

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

cloud-init/cmd/main.go

@@ -0,0 +1,132 @@
+// kubesolo-cloudinit is a lightweight cloud-init parser for KubeSolo OS.
+//
+// It reads a YAML configuration file and applies hostname, network, and
+// KubeSolo settings during the init sequence. Designed to run as a static
+// binary on BusyBox-based systems.
+//
+// Usage:
+//
+//	kubesolo-cloudinit apply <config.yaml>
+//	kubesolo-cloudinit validate <config.yaml>
+//	kubesolo-cloudinit dump <config.yaml>
+package main
+
+import (
+	"encoding/json"
+	"fmt"
+	"log/slog"
+	"os"
+
+	cloudinit "github.com/portainer/kubesolo-os/cloud-init"
+)
+
+const (
+	defaultConfigPath = "/mnt/data/etc-kubesolo/cloud-init.yaml"
+	persistDataDir    = "/mnt/data"
+	configDir         = "/etc/kubesolo"
+)
+
+func main() {
+	// Set up structured logging to stderr (captured by init)
+	slog.SetDefault(slog.New(slog.NewTextHandler(os.Stderr, &slog.HandlerOptions{
+		Level: slog.LevelInfo,
+	})))
+
+	if len(os.Args) < 2 {
+		usage()
+		os.Exit(1)
+	}
+
+	cmd := os.Args[1]
+
+	// Determine config path
+	configPath := defaultConfigPath
+	if len(os.Args) >= 3 {
+		configPath = os.Args[2]
+	}
+
+	switch cmd {
+	case "apply":
+		if err := cmdApply(configPath); err != nil {
+			slog.Error("cloud-init apply failed", "error", err)
+			os.Exit(1)
+		}
+	case "validate":
+		if err := cmdValidate(configPath); err != nil {
+			fmt.Fprintf(os.Stderr, "validation failed: %s\n", err)
+			os.Exit(1)
+		}
+		fmt.Println("OK")
+	case "dump":
+		if err := cmdDump(configPath); err != nil {
+			fmt.Fprintf(os.Stderr, "error: %s\n", err)
+			os.Exit(1)
+		}
+	default:
+		fmt.Fprintf(os.Stderr, "unknown command: %s\n", cmd)
+		usage()
+		os.Exit(1)
+	}
+}
+
+func cmdApply(configPath string) error {
+	slog.Info("applying cloud-init", "config", configPath)
+
+	cfg, err := cloudinit.Parse(configPath)
+	if err != nil {
+		return err
+	}
+
+	// 1. Apply hostname
+	if err := cloudinit.ApplyHostname(cfg); err != nil {
+		return fmt.Errorf("hostname: %w", err)
+	}
+
+	// 2. Apply network configuration
+	if err := cloudinit.ApplyNetwork(cfg); err != nil {
+		return fmt.Errorf("network: %w", err)
+	}
+
+	// 3. Apply KubeSolo settings
+	if err := cloudinit.ApplyKubeSolo(cfg, configDir); err != nil {
+		return fmt.Errorf("kubesolo config: %w", err)
+	}
+
+	// 4. Save persistent configs for next boot
+	if err := cloudinit.SaveHostname(cfg, persistDataDir+"/etc-kubesolo"); err != nil {
+		slog.Warn("failed to save hostname", "error", err)
+	}
+	if err := cloudinit.SaveNetworkConfig(cfg, persistDataDir+"/network"); err != nil {
+		slog.Warn("failed to save network config", "error", err)
+	}
+
+	slog.Info("cloud-init applied successfully")
+	return nil
+}
+
+func cmdValidate(configPath string) error {
+	_, err := cloudinit.Parse(configPath)
+	return err
+}
+
+func cmdDump(configPath string) error {
+	cfg, err := cloudinit.Parse(configPath)
+	if err != nil {
+		return err
+	}
+	enc := json.NewEncoder(os.Stdout)
+	enc.SetIndent("", "  ")
+	return enc.Encode(cfg)
+}
+
+func usage() {
+	fmt.Fprintf(os.Stderr, `Usage: kubesolo-cloudinit <command> [config.yaml]
+
+Commands:
+  apply     Parse and apply cloud-init configuration
+  validate  Check config file for errors
+  dump      Parse and print config as JSON
+
+If config path is omitted, defaults to %s
+`, defaultConfigPath)
+}