[verified] fix: emit UTC-offset last_active so the app can sort by recency

Session-store updated_at values are naive local datetimes; passing them
through without an offset broke Instant.parse() on the client, dropping
last_active and leaving the chat list unsorted after restart.

plugin/pheby/hermes_bridge.py

@@ -210,6 +210,16 @@ def _iso(value: Any) -> Optional[str]:
     try:
         if isinstance(value, (int, float)):
             return dt.datetime.fromtimestamp(value, tz=dt.timezone.utc).isoformat()
+        if isinstance(value, dt.datetime):
+            # Session-store timestamps are naive LOCAL datetimes (see
+            # gateway.session_lifecycle._now). The client parses with
+            # Instant.parse(), which requires an offset — a bare
+            # "2026-09-10T05:41:48" fails and last_active is lost, so the
+            # app can no longer sort by recency. Attach the local offset
+            # and normalize to UTC.
+            if value.tzinfo is None:
+                value = value.astimezone()
+            return value.astimezone(dt.timezone.utc).isoformat()
         return value.isoformat() if value else None
     except (AttributeError, OSError, OverflowError, TypeError, ValueError):
         return None