fix: Add HEAD method support to assets proxy endpoint

- Add HEAD method handler for browser preflight requests
- Use stat_object for HEAD requests (more efficient)
- Return proper headers for HEAD requests
- This fixes 405 errors when browser checks image availability

services/city-service/routes_city.py

@@ -325,7 +325,8 @@ async def update_agent_visibility_endpoint(
 # =============================================================================
 
 @router.get("/assets/proxy/{path:path}")
-async def proxy_asset(path: str):
+@router.head("/assets/proxy/{path:path}")
+async def proxy_asset(path: str, request: Request):
     """
     Proxy endpoint for serving MinIO assets.
     
@@ -352,15 +353,12 @@ async def proxy_asset(path: str):
     try:
         client = get_minio_client()
         
-        # Get object from MinIO
-        # path already contains the full object key (e.g., "microdao/logo/2025/12/02/abc123.png")
-        # ASSETS_BUCKET is prepended by get_object()
-        response = client.get_object(ASSETS_BUCKET, path)
-        
-        # Read data
-        data = response.read()
-        response.close()
-        response.release_conn()
+        # Check if object exists and get metadata
+        try:
+            stat = client.stat_object(ASSETS_BUCKET, path)
+        except Exception as e:
+            logger.warning(f"Asset not found in MinIO: {path}, error: {e}")
+            raise HTTPException(status_code=404, detail="Asset not found")
         
         # Determine content type
         content_type = "application/octet-stream"
@@ -373,14 +371,36 @@ async def proxy_asset(path: str):
         elif path.endswith('.gif'):
             content_type = 'image/gif'
         
+        # For HEAD requests, return headers only
+        if request.method == 'HEAD':
+            from fastapi.responses import Response
+            return Response(
+                status_code=200,
+                headers={
+                    'Content-Type': content_type,
+                    'Content-Length': str(stat.size),
+                    'Cache-Control': 'public, max-age=86400, immutable',
+                    'Access-Control-Allow-Origin': '*',
+                }
+            )
+        
+        # For GET requests, return file data
+        response = client.get_object(ASSETS_BUCKET, path)
+        data = response.read()
+        response.close()
+        response.release_conn()
+        
         return StreamingResponse(
             io.BytesIO(data),
             media_type=content_type,
             headers={
+                'Content-Length': str(stat.size),
                 'Cache-Control': 'public, max-age=86400, immutable',
                 'Access-Control-Allow-Origin': '*',
             }
         )
+    except HTTPException:
+        raise
     except Exception as e:
         logger.error(f"Failed to proxy asset {path}: {e}")
         raise HTTPException(status_code=404, detail="Asset not found")