fix(session): clamp the countdown to wall clock, correct two doc claims

Second review pass (Fable) cleared all six fixes; these are its leftovers.

- _reconcileElapsedTime() runs off the same suspend-blind Stopwatch, so after
  a long device sleep the countdown over-reports - and with the API
  unreachable nothing corrects it, which is precisely the state the app now
  stays in instead of disconnecting. It now takes the lesser of the Stopwatch
  value and the wall-clock deadline; the minimum, so a clock set backwards
  cannot extend a session.
- CHANGELOG claimed the alert covers "the tunnel reporting an error". It
  cannot: AppConfigs.V2RAY_STATES has no error state and the plugin's
  stateName when() ends in else -> "DISCONNECTED", so VpnStatus.error is
  unreachable from the status stream on Android.
- AGENTS.md file map still listed a setSessionExpiry bridge in
  power_settings.dart; no such symbol exists.

Co-Authored-By: Claude Opus 5 <[email protected]>

CHANGELOG.md

@@ -12,8 +12,8 @@ Versions follow [semver](https://semver.org/): MAJOR.MINOR.PATCH
   off the same deadline it already enforces, so the warning still arrives when
   the app is closed, and a support top-up moves it with the deadline.
 - **"Disconnected — not protected" notification** when a session ends without
-  you asking: the 2-hour expiry, the data limit, the server ending the session,
-  or the tunnel reporting an error.
+  you asking: the 2-hour expiry, the data limit, or the server ending the
+  session.
 - **SOCKS5 mode now asks for the notification permission.** It never did,
   because it never raises the VPN consent dialog, so on Android 13+ these
   alerts would have been dropped before they were shown.