feat(docker): switch soul image to engram HTTP mode with entrypoint script

Download both neuron-soul and engram binaries from Artifact Registry.
entrypoint.sh starts engram on :8742, waits for /health, then launches
the soul with ENGRAM_URL set. Removes SOUL_ENGRAM_PATH / file mode.

entrypoint.sh

@@ -0,0 +1,43 @@
+#!/bin/sh
+# entrypoint.sh — start engram then soul, both in a single container.
+#
+# Engram runs as a background HTTP server on localhost:8742.
+# Soul starts once engram reports healthy, with ENGRAM_URL pointing at it.
+#
+# Data directory /data is the PVC mount point — engram reads/writes its
+# snapshot.json (and any future data files) there.
+
+set -eu
+
+ENGRAM_PORT="${ENGRAM_PORT:-8742}"
+ENGRAM_DATA_DIR="${ENGRAM_DATA_DIR:-/data}"
+ENGRAM_HEALTH_URL="http://localhost:${ENGRAM_PORT}/health"
+
+# Ensure the data directory exists (PVC may be mounted but empty on first boot)
+mkdir -p "$ENGRAM_DATA_DIR"
+
+# Start engram in the background
+echo "[entrypoint] starting engram on :${ENGRAM_PORT} data_dir=${ENGRAM_DATA_DIR}"
+ENGRAM_BIND=":${ENGRAM_PORT}" \
+ENGRAM_DATA_DIR="$ENGRAM_DATA_DIR" \
+  /usr/local/bin/engram &
+
+ENGRAM_PID=$!
+
+# Wait for engram to become healthy (up to 30s)
+echo "[entrypoint] waiting for engram..."
+TRIES=0
+until curl -sf "$ENGRAM_HEALTH_URL" > /dev/null 2>&1; do
+    TRIES=$((TRIES + 1))
+    if [ "$TRIES" -ge 30 ]; then
+        echo "[entrypoint] ERROR: engram did not become healthy after 30s" >&2
+        kill "$ENGRAM_PID" 2>/dev/null || true
+        exit 1
+    fi
+    sleep 1
+done
+echo "[entrypoint] engram ready"
+
+# Start soul — it takes over as PID 1's foreground process.
+# SOUL_ENGRAM_PATH must NOT be set; ENGRAM_URL triggers HTTP mode.
+exec /usr/local/bin/neuron