fix: auto-install frontend deps in build script

Add npm install check to build_gui() — if node_modules/ is missing
or doesn't match package-lock.json, install dependencies before building.

scripts/build.sh

@@ -13,8 +13,14 @@ BUILD_DIR="build"
 build_gui() {
   echo "==> Building GUI binary..."
 
-  # Build frontend
-  cd frontend && npm run build && cd ..
+  # Ensure frontend dependencies are installed
+  cd frontend
+  if [ ! -d "node_modules" ] || [ ! -f "node_modules/.package-lock.json" ]; then
+    echo "==> Installing frontend dependencies..."
+    npm install
+  fi
+  npm run build
+  cd ..
 
   # Copy frontend dist to Wails embed directory
   rm -rf cmd/verstak-gui/frontend-dist