fix: address review findings

Dockerfile

@@ -66,7 +66,9 @@ FROM debian:trixie-slim
 
 RUN apt-get update && apt-get install -y --no-install-recommends \
     ca-certificates curl \
-    && rm -rf /var/lib/apt/lists/*
+    && rm -rf /var/lib/apt/lists/* \
+    && groupadd --system app \
+    && useradd --system --gid app --home-dir /nonexistent --shell /usr/sbin/nologin app
 
 COPY --from=builder /usr/local/bin/pokedex-api /usr/local/bin/pokedex-api
 
@@ -75,6 +77,7 @@ ENV GIT_SHA=$GIT_SHA \
     BIND_ADDR=0.0.0.0:5000
 
 EXPOSE 5000
+USER app
 HEALTHCHECK --interval=30s --timeout=3s --start-period=5s --retries=3 \
     CMD curl -fsS http://127.0.0.1:5000/health || exit 1