fix(web): bound a pending #session= link and retire it on Home or a web tab (#507 review)

- A #session=<id> link whose session never appears (closed, a typo, or
  another user's session in multi-user mode) is dropped after
  URL_SESSION_WAIT_MS (30 s) with a "Session not found" toast instead of
  waiting forever. One stored timer per link, cleared whenever the link is
  followed, replaced by a newer link, or retired.
- goHome() and opening a web tab now retire a waiting link, so a session
  that turns up later no longer takes the screen. App-made web tab opens
  (frame self-recovery, the fallback after the active web tab closes) pass
  auto: true and keep it, as selectSession() does.
- zh-CN translation for the new toast.
- selectSession's auto: true comment now lists the #session=<id> link.
- docs: the 30 s bound, a win.location.replace() tip that avoids piling up
  history entries, and the fragment declared a stable SemVer surface in
  versioning-policy.md.
- Tests: timeout drops and toasts, an early arrival is still selected, the
  wait does not restart, goHome and a web tab retire it, an auto web tab
  open keeps it.

Co-Authored-By: Claude Opus 5.5 (1M context) <noreply@anthropic.com>

docs/versioning-policy.md

@@ -40,6 +40,10 @@ A **MAJOR** bump is required to break any of these after 1.0:
    optional fields, new error codes, new SSE events) are non-breaking; breaking
    changes ship under a new prefix (`/api/v2`). The unversioned `/api/...` alias
    is kept working for the bundled UI.
+5. **The dashboard's `#session=<id>` link.** Opening the dashboard URL with a
+   `#session=<id>` fragment selects that session if this client can see it. The
+   fragment name and that meaning are stable; see
+   [Opening a session from your own page](extending-codeman.md#opening-a-session-from-your-own-page).
 
 ## What SemVer does NOT cover (internal surfaces — may change in any release)