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>

Makefile

@@ -1,5 +1,6 @@
-.PHONY: all fetch rootfs initramfs iso disk-image \
+.PHONY: all fetch build-cloudinit rootfs initramfs iso disk-image \
        test-boot test-k8s test-persistence test-deploy test-storage test-all \
+       test-cloudinit \
        dev-vm dev-vm-shell quick docker-build shellcheck \
        kernel-audit clean distclean help
 
@@ -27,7 +28,11 @@ fetch:
 # =============================================================================
 # Build stages
 # =============================================================================
-rootfs: fetch
+build-cloudinit:
+	@echo "==> Building cloud-init binary..."
+	$(BUILD_DIR)/scripts/build-cloudinit.sh
+
+rootfs: fetch build-cloudinit
 	@echo "==> Preparing rootfs..."
 	$(BUILD_DIR)/scripts/extract-core.sh
 	$(BUILD_DIR)/scripts/inject-kubesolo.sh
@@ -78,6 +83,11 @@ test-storage: iso
 
 test-all: test-boot test-k8s test-persistence
 
+# Cloud-init Go tests
+test-cloudinit:
+	@echo "==> Testing cloud-init parser..."
+	cd cloud-init && go test ./... -v -count=1
+
 # Full integration test suite (requires more time)
 test-integration: test-k8s test-deploy test-storage
 
@@ -148,6 +158,7 @@ help:
 	@echo ""
 	@echo "Build targets:"
 	@echo "  make fetch          Download Tiny Core ISO, KubeSolo, dependencies"
+	@echo "  make build-cloudinit Build cloud-init Go binary"
 	@echo "  make rootfs         Extract + prepare rootfs with KubeSolo"
 	@echo "  make initramfs      Repack rootfs into kubesolo-os.gz"
 	@echo "  make iso            Create bootable ISO (default target)"
@@ -161,6 +172,7 @@ help:
 	@echo "  make test-persist   Reboot disk image, verify state persists"
 	@echo "  make test-deploy    Deploy nginx pod, verify Running"
 	@echo "  make test-storage   Test PVC with local-path provisioner"
+	@echo "  make test-cloudinit Run cloud-init Go unit tests"
 	@echo "  make test-all       Run core tests (boot + k8s + persistence)"
 	@echo "  make test-integ     Run full integration suite"
 	@echo ""