Add suitbuilder backend improvements and SSE streaming fix

- Add dedicated streaming proxy endpoint for real-time suitbuilder SSE updates
- Implement stable sorting with character_name and name tiebreakers for deterministic results
- Refactor locked items to locked slots supporting set_id and spell constraints
- Add Mag-SuitBuilder style branch pruning tracking variables
- Enhance search with phase updates and detailed progress logging
- Update design document with SSE streaming proxy fix details

Co-Authored-By: Claude Sonnet 4.5 <noreply@anthropic.com>

main.py

@@ -18,7 +18,7 @@ import socket
 import struct
 
 from fastapi import FastAPI, Header, HTTPException, Query, WebSocket, WebSocketDisconnect, Request
-from fastapi.responses import JSONResponse, Response
+from fastapi.responses import JSONResponse, Response, StreamingResponse
 from fastapi.routing import APIRoute
 from fastapi.staticfiles import StaticFiles
 from fastapi.encoders import jsonable_encoder
@@ -2268,13 +2268,50 @@ async def test_inventory_route():
     """Test route to verify inventory proxy is working"""
     return {"message": "Inventory proxy route is working"}
 
+@app.post("/inv/suitbuilder/search")
+async def proxy_suitbuilder_search(request: Request):
+    """Stream suitbuilder search results - SSE requires streaming proxy."""
+    inventory_service_url = os.getenv('INVENTORY_SERVICE_URL', 'http://inventory-service:8000')
+    logger.info(f"Streaming proxy to suitbuilder search")
+
+    # Read body BEFORE creating generator (request context needed)
+    body = await request.body()
+
+    async def stream_response():
+        try:
+            # Use streaming request with long timeout for searches
+            async with httpx.AsyncClient(timeout=httpx.Timeout(300.0, connect=10.0)) as client:
+                async with client.stream(
+                    method="POST",
+                    url=f"{inventory_service_url}/suitbuilder/search",
+                    content=body,
+                    headers={"Content-Type": "application/json"}
+                ) as response:
+                    async for chunk in response.aiter_bytes():
+                        yield chunk
+        except httpx.ReadTimeout:
+            yield b"event: error\ndata: {\"message\": \"Search timeout\"}\n\n"
+        except Exception as e:
+            logger.error(f"Streaming proxy error: {e}")
+            yield f"event: error\ndata: {{\"message\": \"Proxy error: {str(e)}\"}}\n\n".encode()
+
+    return StreamingResponse(
+        stream_response(),
+        media_type="text/event-stream",
+        headers={
+            "Cache-Control": "no-cache",
+            "Connection": "keep-alive",
+            "X-Accel-Buffering": "no"  # Disable nginx buffering
+        }
+    )
+
 @app.api_route("/inv/{path:path}", methods=["GET", "POST"])
 async def proxy_inventory_service(path: str, request: Request):
     """Proxy all inventory service requests"""
     try:
         inventory_service_url = os.getenv('INVENTORY_SERVICE_URL', 'http://inventory-service:8000')
         logger.info(f"Proxying to inventory service: {inventory_service_url}/{path}")
-        
+
         # Forward the request to inventory service (60s timeout for large queries)
         async with httpx.AsyncClient(timeout=60.0) as client:
             response = await client.request(