Add @spaces.GPU decorator to fix HF Spaces runtime error

HuggingFace Spaces requires at least one @spaces.GPU decorated function
when GPU hardware is detected (from sentence-transformers).

Added a dummy GPU warmup function to satisfy this requirement.

🤖 Generated with [Claude Code](https://claude.com/claude-code)

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

app_unified.py

@@ -6,6 +6,13 @@ import logging
 from pathlib import Path
 from typing import Tuple
 
+# Import spaces for HuggingFace GPU decorator
+try:
+    import spaces
+    HF_SPACES = True
+except ImportError:
+    HF_SPACES = False
+
 # Simple mode imports
 from openai import OpenAI
 from src.config import get_config
@@ -22,6 +29,14 @@ logging.basicConfig(level=logging.INFO)
 logger = logging.getLogger(__name__)
 
 
+# Dummy GPU function to satisfy HuggingFace Spaces GPU check
+if HF_SPACES:
+    @spaces.GPU
+    def _hf_spaces_gpu_warmup():
+        """Dummy function to satisfy HF Spaces GPU decorator requirement."""
+        return "GPU ready"
+
+
 class UnifiedAssistant:
     """Unified assistant supporting both simple and multi-agent modes."""