The supervisor LLM now embeds <type>[id1,id2]</type> entity tags in its
response text. The HomeFormatter buffers streamed tokens, detects complete
tags across chunk boundaries, and emits WsStreamBlock with entity type +
specific IDs. This replaces the old approach of emitting blocks for every
tool_end event, which dumped ALL entities regardless of relevance.
Also fixes:
- NoneType guard on metadata in _run_graph_stream (metadata can be None)
- Updated _HOME_SYSTEM prompt with entity tag instructions
- Updated all affected tests