feat: add security hardening, AppArmor, and ARM64 Raspberry Pi support (Phase 6)

Security hardening: bind kubeconfig server to localhost, mount hardening
(noexec/nosuid/nodev on tmpfs), sysctl network hardening, kernel module
loading lock after boot, SHA256 checksum verification for downloads,
kernel AppArmor + Audit support, complain-mode AppArmor profiles for
containerd and kubelet, and security integration test.

ARM64 Raspberry Pi support: piCore64 base extraction, RPi kernel build
from raspberrypi/linux fork, RPi firmware fetch, SD card image with 4-
partition GPT and tryboot A/B mechanism, BootEnv Go interface abstracting
GRUB vs RPi boot environments, architecture-aware build scripts, QEMU
aarch64 dev VM and boot test.

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

init/init.sh

@@ -64,6 +64,7 @@ export KUBESOLO_CLOUDINIT=""
 export KUBESOLO_EXTRA_FLAGS=""
 export KUBESOLO_PORTAINER_EDGE_ID=""
 export KUBESOLO_PORTAINER_EDGE_KEY=""
+export KUBESOLO_NOAPPARMOR=""
 
 # --- Logging ---
 log() {