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/config.go

@@ -0,0 +1,62 @@
+// Package cloudinit implements a lightweight cloud-init parser for KubeSolo OS.
+//
+// It reads a simplified cloud-init YAML config and applies:
+//   - hostname
+//   - network configuration (static IP or DHCP)
+//   - KubeSolo extra flags and settings
+//   - NTP servers
+//
+// The config file is typically at /mnt/data/etc-kubesolo/cloud-init.yaml
+// or specified via kubesolo.cloudinit= boot parameter.
+package cloudinit
+
+// Config is the top-level cloud-init configuration.
+type Config struct {
+	Hostname string          `yaml:"hostname"`
+	Network  NetworkConfig   `yaml:"network"`
+	KubeSolo KubeSoloConfig  `yaml:"kubesolo"`
+	NTP      NTPConfig       `yaml:"ntp"`
+	Airgap   AirgapConfig    `yaml:"airgap"`
+	Portainer PortainerConfig `yaml:"portainer"`
+}
+
+// NetworkConfig defines network settings.
+type NetworkConfig struct {
+	Mode      string   `yaml:"mode"`      // "dhcp" or "static"
+	Interface string   `yaml:"interface"` // e.g. "eth0" (auto-detected if empty)
+	Address   string   `yaml:"address"`   // CIDR notation, e.g. "192.168.1.100/24"
+	Gateway   string   `yaml:"gateway"`   // e.g. "192.168.1.1"
+	DNS       []string `yaml:"dns"`       // nameservers
+}
+
+// KubeSoloConfig defines KubeSolo-specific settings.
+type KubeSoloConfig struct {
+	ExtraFlags   string   `yaml:"extra-flags"`
+	LocalStorage *bool    `yaml:"local-storage"`
+	ExtraSANs    []string `yaml:"apiserver-extra-sans"`
+}
+
+// NTPConfig defines NTP settings.
+type NTPConfig struct {
+	Servers []string `yaml:"servers"`
+}
+
+// AirgapConfig defines air-gapped deployment settings.
+type AirgapConfig struct {
+	ImportImages bool   `yaml:"import-images"`
+	ImagesDir    string `yaml:"images-dir"`
+}
+
+// PortainerConfig defines Portainer Edge Agent settings.
+type PortainerConfig struct {
+	EdgeAgent EdgeAgentConfig `yaml:"edge-agent"`
+}
+
+// EdgeAgentConfig holds Portainer Edge Agent connection details.
+type EdgeAgentConfig struct {
+	Enabled     bool   `yaml:"enabled"`
+	EdgeID      string `yaml:"edge-id"`
+	EdgeKey     string `yaml:"edge-key"`
+	PortainerURL string `yaml:"portainer-url"`
+	Image       string `yaml:"image"`
+}