fix: always set kv_port in configure_ports to prevent TypeError

The overwrite_args function always uses config.kv_port regardless of
prefix caching settings, so configure_ports must always set this value
to prevent "NoneType and int" TypeError.

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

Co-Authored-By: Claude <[email protected]>

Author: nnshah1

examples/multimodal/utils/args.py

@@ -139,8 +139,8 @@ def ensure_side_channel_host():
 def configure_ports(config: Config):
     """Configure port settings from dedicated environment overrides."""
 
-    if config.engine_args.enable_prefix_caching:
-        config.kv_port = get_kv_port()
+    # Always set kv_port as it's used by overwrite_args regardless of prefix caching
+    config.kv_port = get_kv_port()
 
     ensure_side_channel_host()