fix(gateway): classify SimpleX non-image/non-audio files as DOCUMENT

SimpleX tagged unknown files application/octet-stream in media_types
but classification only handled audio/image, leaving msg_type TEXT —
run.py never injected the document context. Same bug class as #12845.

plugins/platforms/simplex/adapter.py

@@ -625,6 +625,11 @@ class SimplexAdapter(BasePlatformAdapter):
                 msg_type = MessageType.VOICE
             elif any(mt.startswith("image/") for mt in media_types):
                 msg_type = MessageType.PHOTO
+            else:
+                # Catch-all: non-image/non-audio files (tagged
+                # application/octet-stream above) are documents so run.py's
+                # document-context injection surfaces the file to the agent.
+                msg_type = MessageType.DOCUMENT
 
         # Timestamp
         ts_str = meta.get("itemTs") or meta.get("createdAt", "")