fix: default distributions to automatic GPU support with CPU fallback

tools/embeddinggemma2/build_runtime.py

@@ -17,7 +17,7 @@ def run(arguments, cwd=None):
 
 def main():
     parser = argparse.ArgumentParser(description="Build Searchi's pinned Google embedding worker")
-    parser.add_argument("--backend", choices=["cpu", "auto", "metal", "vulkan", "cuda"], default="cpu")
+    parser.add_argument("--backend", choices=["cpu", "auto", "metal", "vulkan", "cuda"], default="auto")
     parser.add_argument("--jobs", type=int, default=2)
     args = parser.parse_args()
     if not 1 <= args.jobs <= 16: