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/kubesolo.go

@@ -0,0 +1,79 @@
+package cloudinit
+
+import (
+	"fmt"
+	"log/slog"
+	"os"
+	"path/filepath"
+	"strings"
+)
+
+// ApplyKubeSolo writes KubeSolo configuration files based on cloud-init config.
+// These files are read by init stage 90-kubesolo.sh when building the
+// KubeSolo command line.
+func ApplyKubeSolo(cfg *Config, configDir string) error {
+	if err := os.MkdirAll(configDir, 0o755); err != nil {
+		return fmt.Errorf("creating config dir %s: %w", configDir, err)
+	}
+
+	// Write extra flags file (consumed by 90-kubesolo.sh)
+	flags := buildExtraFlags(cfg)
+	if flags != "" {
+		flagsPath := filepath.Join(configDir, "extra-flags")
+		if err := os.WriteFile(flagsPath, []byte(flags+"\n"), 0o644); err != nil {
+			return fmt.Errorf("writing extra-flags: %w", err)
+		}
+		slog.Info("wrote KubeSolo extra flags", "path", flagsPath, "flags", flags)
+	}
+
+	// Write config.yaml for KubeSolo if we have settings beyond defaults
+	if err := writeKubeSoloConfig(cfg, configDir); err != nil {
+		return err
+	}
+
+	return nil
+}
+
+func buildExtraFlags(cfg *Config) string {
+	var parts []string
+
+	if cfg.KubeSolo.ExtraFlags != "" {
+		parts = append(parts, cfg.KubeSolo.ExtraFlags)
+	}
+
+	// Add extra SANs from cloud-init
+	for _, san := range cfg.KubeSolo.ExtraSANs {
+		parts = append(parts, "--apiserver-extra-sans", san)
+	}
+
+	return strings.Join(parts, " ")
+}
+
+func writeKubeSoloConfig(cfg *Config, configDir string) error {
+	var lines []string
+	lines = append(lines, "# Generated by KubeSolo OS cloud-init")
+	lines = append(lines, "data-dir: /var/lib/kubesolo")
+
+	if cfg.KubeSolo.LocalStorage != nil {
+		if *cfg.KubeSolo.LocalStorage {
+			lines = append(lines, "local-storage: true")
+		} else {
+			lines = append(lines, "local-storage: false")
+		}
+	} else {
+		lines = append(lines, "local-storage: true")
+	}
+
+	lines = append(lines, "bind-address: 0.0.0.0")
+	lines = append(lines, "cluster-cidr: 10.42.0.0/16")
+	lines = append(lines, "service-cidr: 10.43.0.0/16")
+
+	dest := filepath.Join(configDir, "config.yaml")
+	content := strings.Join(lines, "\n") + "\n"
+	if err := os.WriteFile(dest, []byte(content), 0o644); err != nil {
+		return fmt.Errorf("writing config.yaml: %w", err)
+	}
+
+	slog.Info("wrote KubeSolo config", "path", dest)
+	return nil
+}