fix: use venv python for JupyterLab — system python3 lacks jupyterlab

jupyterlab is installed into /opt/hermes/.venv, not system python3.
start_jupyter() was calling python3 -c "import jupyterlab" which fails
on system python → returned 1 → set -euo pipefail killed start.sh →
container crashed every boot → HF Space stuck in RUNNING_APP_STARTING.

Fixes:
- Use /opt/hermes/.venv/bin/python for the import check and launch
- Change failing return 1s in start_jupyter to return 0 (non-fatal)
- Restore HEALTHCHECK with 60s start-period (was accidentally removed)

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

Dockerfile

@@ -97,6 +97,7 @@ ENV HERMES_HOME=/opt/data \
 
 EXPOSE 7861
 
-HEALTHCHECK NONE
+HEALTHCHECK --interval=30s --timeout=5s --start-period=60s \
+  CMD curl -fsS http://localhost:7861/health || exit 1
 
 CMD ["/opt/huggingmes/start.sh"]

start.sh

@@ -318,18 +318,19 @@ start_jupyter() {
   local token="${JUPYTER_TOKEN:-${API_SERVER_KEY:-}}"
   if [ -z "$token" ]; then
     echo "WARNING: No GATEWAY_TOKEN or JUPYTER_TOKEN set — JupyterLab skipped (terminal would be unauthenticated)." >&2
-    return 1
+    return 0
   fi
   export JUPYTER_TOKEN="$token"
-  if ! python3 -c "import jupyterlab" >/dev/null 2>&1; then
-    echo "WARNING: jupyterlab not installed; skipping terminal." >&2
-    return 1
+  local VENV_PYTHON="/opt/hermes/.venv/bin/python"
+  if ! "$VENV_PYTHON" -c "import jupyterlab" >/dev/null 2>&1; then
+    echo "WARNING: jupyterlab not installed in venv; skipping terminal." >&2
+    return 0
   fi
   local root_dir="${JUPYTER_ROOT_DIR:-$HERMES_HOME/workspace}"
   mkdir -p "$root_dir"
   ln -sfn "$HERMES_HOME" "$root_dir/HuggingMes" 2>/dev/null || true
   echo "Starting JupyterLab terminal on port 8888 (path: /terminal/) root: $root_dir"
-  python3 -m jupyterlab \
+  "$VENV_PYTHON" -m jupyterlab \
     --ip 127.0.0.1 \
     --port 8888 \
     --no-browser \