fix(gateway): honor queue mode in runner PRIORITY interrupt path

When display.busy_input_mode is 'queue', the runner-level PRIORITY block
in _handle_message was still calling running_agent.interrupt() for every
text follow-up to an active session. The adapter-level busy handler
already honors queue mode (commit 9d147f7fd), but this runner-level path
was an unconditional interrupt regardless of config.

Adds a queue-mode branch that queues the follow-up via
_queue_or_replace_pending_event() and returns without interrupting.

Salvages the useful part of #12070 (@knockyai). The config fan-out to
per-platform extra was redundant — runner already loads busy_input_mode
directly via _load_busy_input_mode().

gateway/run.py

@@ -3591,6 +3591,10 @@ class GatewayRunner:
                     if self._queue_during_drain_enabled()
                     else f"⏳ Gateway is {self._status_action_gerund()} and is not accepting another turn right now."
                 )
+            if self._busy_input_mode == "queue":
+                logger.debug("PRIORITY queue follow-up for session %s", _quick_key[:20])
+                self._queue_or_replace_pending_event(_quick_key, event)
+                return None
             logger.debug("PRIORITY interrupt for session %s", _quick_key[:20])
             running_agent.interrupt(event.text)
             if _quick_key in self._pending_messages: