Add an experimental Alpine image flow

Stage a complete Alpine x86_64 image stack so \	--image alpineworks like the existing manual Void path instead of relying on Debian-oriented image builds.\n\nAdd make targets plus kernel/rootfs/register helpers that download pinned Alpine artifacts, extract a Firecracker-compatible vmlinux, build a matching mkinitfs initramfs, seed OpenRC services, and register/promote a managed image named alpine.\n\nFold in the bring-up fixes discovered during boot validation: use rootfstype=ext4 in shared boot args, install libgcc/libstdc++ for the opencode binary, and give opencode more time to become ready on cold boots.\n\nValidate with go test ./..., the Alpine helper builds, image promotion, and banger vm create --image alpine --name alp --nat plus guest service and port checks.

examples/alpine.config.toml

@@ -0,0 +1,9 @@
+# Experimental Alpine Linux guest profile for local testing.
+#
+# Register or promote a complete `alpine` image first, then point the daemon
+# at it by name. Firecracker is resolved from PATH by default; set
+# `firecracker_bin` only if you need an override.
+
+default_image_name = "alpine"
+# firecracker_bin = "/usr/bin/firecracker"
+# ssh_key_path = "/abs/path/to/private/key"