Fix Docker build: move entrypoint out of excluded deploy/ dir

.dockerignore excludes deploy/ entirely. The entrypoint script lived
there, so the COPY in Stage 3 failed with "not found". Move it to the
project root (alongside Dockerfile) where the build context includes it.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

docker-entrypoint.sh

@@ -0,0 +1,11 @@
+#!/bin/sh
+set -e
+
+if [ "${RUN_MIGRATIONS:-true}" = "true" ]; then
+  echo "running migrations..."
+  node /app/scripts/migrate.mjs
+else
+  echo "skipping migrations (RUN_MIGRATIONS=$RUN_MIGRATIONS)"
+fi
+
+exec node /app/server.js