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>

src/web/public/i18n.js

@@ -571,6 +571,8 @@
     'Task Complete': '任务完成',
     'Copied to clipboard': '已复制到剪贴板',
     'Nothing to copy': '没有可复制的内容',
+    // A `#session=<id>` link whose session never appeared (app.js _armUrlSessionWait).
+    'Session not found': '未找到会话',
     // Terminal touch-selection bar (long-press to select). The bar is a sibling of
     // `.xterm`, not a descendant, so SKIP_SELECTOR does not cover it and these apply.
     Copy: '复制',