fix(chat): broadcast SSE HITL resume to thread subscribers

[huangcheng]

Problem

A HITL pause resolved outside a dashboard page (SSE resume from another client, IM, or API) left the page's approval/ask card visible until a manual reload.

Root cause: turns initiated over WebSocket broadcast their chunks to the thread's subscribers (ws_channel → hub.push_to_thread), but the SSE resume path (POST /agents/{agent_id}/chat/hitl/resume) only streamed to the HTTP caller — open pages never learned the pause was resolved elsewhere.

Fix

Mirror the ws_channel contract in iter_dashboard_hitl_resume_sse (src/octop/api/routers/chat/routes.py):

• While streaming the resumed turn, push every chunk (plus done, and error+done on failure) to the thread's WebSocket subscribers.
• Keep the hub's turn flag in sync (mark_turn_active / mark_turn_idle) so history turn_active stays accurate for SSE resumes too.
• Delivery failures are logged and never abort the harness turn (same contract as ws_channel).
• Subscribers keep receiving frames even after the SSE client disconnects (the turn continues server-side by design).

No frontend change needed: subscribed pages are already driven by WS frames, so the pending card dismisses in place.

Verification

• New unit tests in tests/unit/api/test_chat_hitl_resume.py (real WebSocketHub + fake subscriber):
  • chunks + done are broadcast in order and the turn flag returns to idle;
  • broadcast continues after the SSE client disconnects.
• Gates run manually: ruff check/format, mypy --strict src/octop, full pytest -m "not live" — green (committed with SKIP_PRECOMMIT=1 because make is unavailable in this Windows shell; the equivalent checks were run manually).
• Live verification against a real model turn (MiniMax): pending ask_user_question card on an open page dismissed without reload after the pause was answered out-of-band via the API; the page continued streaming the resumed turn.

[jubaoliang]

分诊：问题真实（SSE HITL resume 不 push_to_thread，页外解决后面卡片卡住）。

请 rebase，CHANGELOG 改成中文并放到当前 Unreleased。CI 已绿。