feat(web): show machine + last-active in session detail header (#1244)

* feat(web): show machine and last-active in session header

Multi-machine estates lose the machine signal after leaving list filter
chips; surface machine label + relative age in SessionHeader meta row.
Fixes #1241.

Co-authored-by: Cursor <cursoragent@cursor.com>

* fix(web): keep session-header age fresh under keep-alive

Treat detail-cache activeAt keep-alives as render-relevant now that the
header reads them, and tick relative age every minute so labels advance
without a session prop change.

Co-authored-by: Cursor <cursoragent@cursor.com>

* fix(web): skip sub-minute activeAt keep-alives in detail cache

Relative age only changes at 60s boundaries; accepting every ~10s
heartbeat replaced the Session object and re-rendered the chat tree
for no visible header change.

Co-authored-by: Cursor <cursoragent@cursor.com>

* chore: retrigger Codex PR review after stream disconnect

Co-authored-by: Cursor <cursoragent@cursor.com>

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Co-authored-by: Cursor <cursoragent@cursor.com>

web/src/lib/locales/zh-CN.ts

@@ -128,6 +128,7 @@ export default {
   'session.item.path': '路径',
   'session.item.agent': '代理',
   'session.item.model': '模型',
+  'session.item.machine': '机器',
   'session.item.worktree': '工作树',
   'session.item.pending': '待处理',
   'session.item.thinking': '思考中',