Fix livebook path resolution in bin/notebook

Falls back to mix escripts directory when livebook isn't in PATH.

bin/notebook

@@ -11,6 +11,13 @@ COOKIE="microwaveprop_nb"
 NODE="prop@$(hostname -s)"
 PORT="${LIVEBOOK_PORT:-8081}"
 
+# Find livebook: PATH, then mix escripts dir
+LIVEBOOK="$(command -v livebook 2>/dev/null || echo "$(elixir -e 'IO.write(Path.join(Mix.path_for(:escripts), "livebook"))')")"
+if [ ! -x "$LIVEBOOK" ]; then
+  echo "Livebook not found. Install with: mix escript.install hex livebook"
+  exit 1
+fi
+
 echo "Starting Phoenix on :4000 and Livebook on :${PORT}..."
 echo "Livebook will be at http://localhost:${PORT}"
 echo ""
@@ -27,7 +34,7 @@ sleep 3
 LIVEBOOK_HOME="$(pwd)/notebooks" \
 LIVEBOOK_APPS_PATH="$(pwd)/notebooks" \
 LIVEBOOK_APPS_PATH_HUB_ID="personal-hub" \
-  livebook server \
+  "$LIVEBOOK" server \
   --port "$PORT" \
   --default-runtime "attached:${NODE}:${COOKIE}" &
 LIVEBOOK_PID=$!