Rename experimental Void image to void

Replace the old `void-exp` repository defaults with `void` so the Make targets,
registration helper, example config, verification messaging, and sample test
fixtures all line up with the new managed image name.

Keep the scope to repo-facing naming only: config overrides, helper output, and
test fixtures now expect `void`, while runtime compatibility for existing local
`void-exp` VMs remains an operational concern outside this commit.

Validation: go test ./..., make build, and a local `banger vm create --image void`
smoke boot with ssh and opencode ports up.

scripts/make-rootfs-void.sh

@@ -590,4 +590,4 @@ log "building work-seed $WORK_SEED"
 BUILD_DONE=1
 log "built experimental Void rootfs: $OUT_ROOTFS"
 log "built experimental Void work-seed: $WORK_SEED"
-log "use examples/void-exp.config.toml as the local config override template"
+log "use examples/void.config.toml as the local config override template"

scripts/register-void-image.sh

@@ -46,7 +46,7 @@ resolve_banger_bin() {
 SCRIPT_DIR="$(cd "$(dirname "${BASH_SOURCE[0]}")" && pwd)"
 REPO_ROOT="$(cd "$SCRIPT_DIR/.." && pwd)"
 RUNTIME_DIR="${BANGER_MANUAL_DIR:-$REPO_ROOT/build/manual}"
-IMAGE_NAME="${VOID_IMAGE_NAME:-void-exp}"
+IMAGE_NAME="${VOID_IMAGE_NAME:-void}"
 BANGER_BIN="$(resolve_banger_bin)"
 ROOTFS="$RUNTIME_DIR/rootfs-void.ext4"
 WORK_SEED="$RUNTIME_DIR/rootfs-void.work-seed.ext4"

scripts/verify.sh

@@ -171,7 +171,7 @@ Usage: ./scripts/verify.sh [--nat] [--image <name>]
 
 Run a basic smoke test for the Go VM workflow.
 Use --nat to additionally verify outbound NAT and host rule cleanup.
-Use --image to verify a non-default image such as void-exp.
+Use --image to verify a non-default image such as void.
 EOF
 }