Sse Stream

Server-Sent Events endpoint that pushes data updates as they are fetched.

Pushes cached headlines + indicators immediately on connect, then streams live events (headlines, indicators, ticker updates, market-pulse) as they arrive via shared.sse_broadcast().

WP-G (2026-09-26 external review, P1-1): each session's queue now lives on the event loop (services/sse_session_queue.py), fed from the broadcaster's threads via loop.call_soon_threadsafe. It used to be a queue.Queue polled with asyncio.to_thread(q.get, True, 15), which pinned one default-executor thread per open stream: ~32 streams starved every other to_thread call in the process. sse_broadcast() is unchanged -- it still calls put_nowait and still drops a client whose queue is full.