fix: thread gateway user_id to memory plugins for per-user scoping (#5895)

Memory plugins (Mem0, Honcho) used static identifiers ('hermes-user',
config peerName) meaning all gateway users shared the same memory bucket.

Changes:
- AIAgent.__init__: add user_id parameter, store as self._user_id
- run_agent.py: include user_id in _init_kwargs passed to memory providers
- gateway/run.py: pass source.user_id to AIAgent in primary + background paths
- Mem0 plugin: prefer kwargs user_id over config default
- Honcho plugin: override cfg.peer_name with gateway user_id when present

CLI sessions (user_id=None) preserve existing defaults. Only gateway
sessions with a real platform user_id get per-user memory scoping.

Reported by plev333.

plugins/memory/honcho/__init__.py

@@ -216,6 +216,12 @@ class HonchoMemoryProvider(MemoryProvider):
                 logger.debug("Honcho not configured — plugin inactive")
                 return
 
+            # Override peer_name with gateway user_id for per-user memory scoping.
+            # CLI sessions won't have user_id, so the config default is preserved.
+            _gw_user_id = kwargs.get("user_id")
+            if _gw_user_id:
+                cfg.peer_name = _gw_user_id
+
             self._config = cfg
 
             # ----- B1: recall_mode from config -----