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.

run_agent.py

@@ -526,6 +526,7 @@ class AIAgent:
         reasoning_config: Dict[str, Any] = None,
         prefill_messages: List[Dict[str, Any]] = None,
         platform: str = None,
+        user_id: str = None,
         skip_context_files: bool = False,
         skip_memory: bool = False,
         session_db=None,
@@ -590,6 +591,7 @@ class AIAgent:
         self.quiet_mode = quiet_mode
         self.ephemeral_system_prompt = ephemeral_system_prompt
         self.platform = platform  # "cli", "telegram", "discord", "whatsapp", etc.
+        self._user_id = user_id  # Platform user identifier (gateway sessions)
         # Pluggable print function — CLI replaces this with _cprint so that
         # raw ANSI status lines are routed through prompt_toolkit's renderer
         # instead of going directly to stdout where patch_stdout's StdoutProxy
@@ -1092,6 +1094,9 @@ class AIAgent:
                             "hermes_home": str(_ghh()),
                             "agent_context": "primary",
                         }
+                        # Thread gateway user identity for per-user memory scoping
+                        if self._user_id:
+                            _init_kwargs["user_id"] = self._user_id
                         # Profile identity for per-profile provider scoping
                         try:
                             from hermes_cli.profiles import get_active_profile_name