Bake mise into default VM images

New VMs should have mise available without a per-VM bootstrap step, and the activation needs to work in the default root bash workflow.

Install a pinned mise binary during both the Go-native image build path and the customize.sh rootfs rebuild path, then enable bash activation through /etc/profile.d for login shells and /etc/bash.bashrc for interactive shells.

Add a regression around the generated provisioning script and validate with bash -n customize.sh, go test ./..., and make build. Rebuilding the default rootfs is still required before future default-image VMs pick up the change.

internal/daemon/imagebuild_test.go

@@ -0,0 +1,23 @@
+package daemon
+
+import (
+	"strings"
+	"testing"
+)
+
+func TestBuildProvisionScriptInstallsAndActivatesMise(t *testing.T) {
+	t.Parallel()
+
+	script := buildProvisionScript("devbox", "1.1.1.1", []string{"git", "curl"}, false)
+	for _, snippet := range []string{
+		"curl -fsSL https://mise.run | MISE_INSTALL_PATH='/usr/local/bin/mise' MISE_VERSION='v2025.12.0' sh",
+		"cat > /etc/profile.d/mise.sh <<'EOF'",
+		"if [ -n \"${BASH_VERSION:-}\" ] && [ -x '/usr/local/bin/mise' ]; then",
+		`eval "$(/usr/local/bin/mise activate bash)"`,
+		`if ! grep -Fqx 'eval "$(/usr/local/bin/mise activate bash)"' '/etc/bash.bashrc'; then`,
+	} {
+		if !strings.Contains(script, snippet) {
+			t.Fatalf("buildProvisionScript missing snippet %q\nscript:\n%s", snippet, script)
+		}
+	}
+}