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/extending-codeman.md

@@ -355,7 +355,16 @@ When that window already shows the dashboard, only the fragment differs. The
 browser therefore keeps the page loaded, and the dashboard switches tabs without
 reloading it. A session the window has shown before appears at once. A session
 your page has only just created may not be listed yet, so the dashboard waits
-for its `session:created` event and selects it then.
+for its `session:created` event and selects it then. That wait lasts at most 30
+seconds: a link whose session never appears (a closed session, a typo, or in
+multi-user mode another user's session) is dropped with a "Session not found"
+notice. Clicking another tab, going Home or opening a web tab also ends the
+wait, so a session that turns up later never takes the screen from the person.
+
+When your page holds the window reference (`const win = window.open(...)`),
+prefer `win.location.replace(url)` for later links: it still fires `hashchange`
+without a reload, but adds no history entry, so Back in the dashboard window
+does not turn into a silent no-op.
 
 Following a link does not count as someone looking at the session, so it
 leaves the session's idle alert in place. The alert clears when the person