Claude Code: add /health endpoint to main.py

Fixes "Error: unknown" by adding missing /health endpoint that
HuggingFace Spaces probes for health checks.

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

main.py

@@ -119,6 +119,16 @@ async def root():
     """
 
 
+@app.get("/health")
+async def health():
+    """Health check endpoint for HuggingFace Spaces."""
+    return {
+        "status": "ok",
+        "service": "cain",
+        "timestamp": datetime.utcnow().isoformat()
+    }
+
+
 @app.get("/api/status")
 async def status():
     """Get Cain's current status and personality."""