Reorganize the source checkout layout

Separate tracked source from generated artifacts so the repo root stops accumulating helper scripts, manifests, and local runtime outputs.

Move manual shell entrypoints under scripts/, manifests under config/, and the Firecracker API reference under docs/reference/. Make build and runtimebundle now target build/bin, build/runtime, and build/dist as the canonical source-checkout paths.

Update runtime discovery, helper scripts, tests, and docs to follow the new layout while keeping legacy source-checkout runtime fallbacks for existing local bundles during migration.

Validated with bash -n on the moved scripts, make build, and GOCACHE=/tmp/banger-gocache go test ./....

scripts/register-void-image.sh

@@ -0,0 +1,95 @@
+#!/usr/bin/env bash
+set -euo pipefail
+
+log() {
+  printf '[register-void-image] %s\n' "$*" >&2
+}
+
+find_latest_matching() {
+  local dir="$1"
+  local pattern="$2"
+  if [[ ! -d "$dir" ]]; then
+    return 1
+  fi
+  find "$dir" -maxdepth 1 -type f -name "$pattern" | sort | tail -n 1
+}
+
+find_latest_module_dir() {
+  local root="$1"
+  if [[ ! -d "$root" ]]; then
+    return 1
+  fi
+  find "$root" -mindepth 1 -maxdepth 1 -type d | sort | tail -n 1
+}
+
+resolve_banger_bin() {
+  if [[ -n "${BANGER_BIN:-}" ]]; then
+    printf '%s\n' "$BANGER_BIN"
+    return
+  fi
+  if [[ -x "$REPO_ROOT/build/bin/banger" ]]; then
+    printf '%s\n' "$REPO_ROOT/build/bin/banger"
+    return
+  fi
+  if [[ -x "$REPO_ROOT/banger" ]]; then
+    printf '%s\n' "$REPO_ROOT/banger"
+    return
+  fi
+  if command -v banger >/dev/null 2>&1; then
+    command -v banger
+    return
+  fi
+  log "banger binary not found; build it first with 'make build' or set BANGER_BIN"
+  exit 1
+}
+
+SCRIPT_DIR="$(cd "$(dirname "${BASH_SOURCE[0]}")" && pwd)"
+REPO_ROOT="$(cd "$SCRIPT_DIR/.." && pwd)"
+DEFAULT_RUNTIME_DIR="$REPO_ROOT/build/runtime"
+if [[ ! -d "$DEFAULT_RUNTIME_DIR" && -d "$REPO_ROOT/runtime" ]]; then
+  DEFAULT_RUNTIME_DIR="$REPO_ROOT/runtime"
+fi
+
+RUNTIME_DIR="${BANGER_RUNTIME_DIR:-$DEFAULT_RUNTIME_DIR}"
+IMAGE_NAME="${VOID_IMAGE_NAME:-void-exp}"
+BANGER_BIN="$(resolve_banger_bin)"
+ROOTFS="$RUNTIME_DIR/rootfs-void.ext4"
+WORK_SEED="$RUNTIME_DIR/rootfs-void.work-seed.ext4"
+PACKAGES="$REPO_ROOT/config/packages.void"
+
+if [[ ! -f "$ROOTFS" ]]; then
+  log "missing Void rootfs: $ROOTFS"
+  exit 1
+fi
+if [[ ! -f "$WORK_SEED" ]]; then
+  log "missing Void work-seed: $WORK_SEED"
+  exit 1
+fi
+
+args=(
+  image register
+  --name "$IMAGE_NAME"
+  --rootfs "$ROOTFS"
+  --work-seed "$WORK_SEED"
+  --packages "$PACKAGES"
+)
+
+if [[ ! -d "$RUNTIME_DIR/void-kernel" ]]; then
+  log "missing staged Void kernel artifacts: $RUNTIME_DIR/void-kernel"
+  log "run 'make void-kernel' before registering $IMAGE_NAME"
+  exit 1
+fi
+
+kernel="$(find_latest_matching "$RUNTIME_DIR/void-kernel/boot" 'vmlinux-*' || true)"
+initrd="$(find_latest_matching "$RUNTIME_DIR/void-kernel/boot" 'initramfs-*' || true)"
+modules="$(find_latest_module_dir "$RUNTIME_DIR/void-kernel/lib/modules" || true)"
+
+if [[ -z "$kernel" || -z "$initrd" || -z "$modules" ]]; then
+  log "staged Void kernel is incomplete; expected vmlinux, initramfs, and modules under $RUNTIME_DIR/void-kernel"
+  exit 1
+fi
+
+log "using staged Void kernel artifacts from $RUNTIME_DIR/void-kernel"
+args+=(--kernel "$kernel" --initrd "$initrd" --modules "$modules")
+
+"$BANGER_BIN" "${args[@]}"