feat: configurable port via PORT environment variable (#36)

The listening port was hardcoded to 8080. While Docker port mapping
covers most cases, some orchestrators and reverse proxy setups prefer
the container to listen on a specific port.

Changes:
- entrypoint.sh reads PORT env var with default of 8080
- Dockerfile sets ENV PORT=8080 as the default
- Healthcheck uses ${PORT} so it works with custom ports

Backwards compatible: default behavior is unchanged (port 8080).

Tested with default port (8080) and custom port (PORT=9090),
both return 200 on /healthz.

Fixes #25

Author: gordonmurray

docker/Dockerfile

@@ -33,11 +33,12 @@ USER appuser
 
 ENV PATH=/home/appuser/.local/bin:$PATH
 ENV DATA_PATH=/data
+ENV PORT=8080
 
 EXPOSE 8080
 
 HEALTHCHECK --interval=30s --timeout=10s --start-period=5s --retries=3 \
-    CMD curl -fsS http://localhost:8080/healthz || exit 1
+    CMD curl -fsS http://localhost:${PORT}/healthz || exit 1
 
 # Build arguments for labels (redeclare after FROM)
 ARG LANCEDB_VERSION=0.29.2

docker/entrypoint.sh

@@ -11,7 +11,9 @@ if [ ! -r "$DATA_PATH" ]; then
     exit 1
 fi
 
-echo "Starting Lance Viewer on port 8080..."
+PORT="${PORT:-8080}"
+
+echo "Starting Lance Viewer on port ${PORT}..."
 echo "Data path: $DATA_PATH"
 
-exec python -m uvicorn app:app --host 0.0.0.0 --port 8080
+exec python -m uvicorn app:app --host 0.0.0.0 --port "${PORT}"