docs(api): session list incident_id filter and ref field

[ysyneu]

Documents two additions to POST /safari/session/list:

• Request incident_id: returns sessions about one incident (the bound session, its forks, and the session that absorbed it through on-call incident fan-in while the absorbing rule exists). Intersects with scope / team_ids.
• Response SessionItem.ref: inc_<incident_id> for incident sessions, omitted otherwise.

Updated in en/zh for both safari.openapi.*.json and the consolidated openapi.*.json. No operations added or removed, so docs.json and the api-catalog are unchanged.

🤖 Generated with Claude Code

[ysyneu]

Superseded by #1070, which re-applies the still-relevant parts of this PR on current main (see the table there for what was ported and what was left out).