Fix appuser: pin UID/GID 1000 to match previous image ownership

Author: SFenton

FSTService/Dockerfile

@@ -39,8 +39,10 @@ RUN apt-get update && apt-get install -y --no-install-recommends \
     libglib2.0-0t64 libxkbcommon0 libgl1 libfreetype6 libdbus-1-3 \
     && rm -rf /var/lib/apt/lists/*
 
-# Create non-root user for container hardening
-RUN useradd --no-create-home --home-dir /app --shell /usr/sbin/nologin appuser
+# Create non-root user for container hardening (UID 1000 matches the previous
+# Debian-based image so existing volume files remain writable).
+RUN groupadd --gid 1000 appuser && \
+    useradd --uid 1000 --gid 1000 --no-create-home --home-dir /app --shell /usr/sbin/nologin appuser
 
 # Download CHOpt CLI for path generation (Linux x64) — pinned in tools/chopt-cli-linux/
 COPY tools/chopt-cli-linux/ /app/tools/