feat(agent): real nix (sandbox=false) for firmware SBOM, replacing nix-portable (#159)

docker/agent-entrypoint.sh

@@ -0,0 +1,19 @@
+#!/usr/bin/env bash
+# Seed the nix store on first start, then run the agent.
+#
+# The firmware-SBOM pipeline drives a real `nix` build (tramiton NixBackend).
+# The image ships the store as a bootstrap tarball rather than baking /nix, so a
+# persistent /nix volume (mounted empty on first deploy) gets populated once and
+# then survives redeploys. Seeding is best-effort: if it fails, the agent still
+# starts and firmware SBOMs fall back to analysis-only.
+if [ ! -e /nix/store ]; then
+  echo "agent-entrypoint: seeding /nix store from image bootstrap..."
+  mkdir -p /nix
+  if tar -C / -xzf /opt/nix-bootstrap.tar.gz; then
+    echo "agent-entrypoint: /nix store seeded."
+  else
+    echo "agent-entrypoint: WARN nix seed failed; firmware SBOM will use analysis-only fallback."
+  fi
+fi
+
+exec compliance-agent "$@"