fix: Ollama Cloud auth, /model switch persistence, and alias tab completion

- Add OLLAMA_API_KEY to credential resolution chain for ollama.com endpoints
- Update requested_provider/_explicit_api_key/_explicit_base_url after /model
  switch so _ensure_runtime_credentials() doesn't revert the switch
- Pass base_url/api_key from fallback config to resolve_provider_client()
- Add DirectAlias system: user-configurable model_aliases in config.yaml
  checked before catalog resolution, with reverse lookup by model ID
- Add /model tab completion showing aliases with provider metadata

Co-authored-by: LucidPaths <LucidPaths@users.noreply.github.com>

gateway/run.py

@@ -3393,6 +3393,16 @@ class GatewayRunner:
             except Exception as exc:
                 logger.warning("In-place model switch failed for cached agent: %s", exc)
 
+        # Store a note to prepend to the next user message so the model
+        # knows about the switch (avoids system messages mid-history).
+        if not hasattr(self, "_pending_model_notes"):
+            self._pending_model_notes = {}
+        self._pending_model_notes[session_key] = (
+            f"[Note: model was just switched from {current_model} to {result.new_model} "
+            f"via {result.provider_label or result.target_provider}. "
+            f"Adjust your self-identification accordingly.]"
+        )
+
         # Store session override so next agent creation uses the new model
         if not hasattr(self, "_session_model_overrides"):
             self._session_model_overrides = {}
@@ -6440,6 +6450,12 @@ class GatewayRunner:
                 except Exception as _e:
                     logger.error("Failed to send approval request: %s", _e)
 
+            # Prepend pending model switch note so the model knows about the switch
+            _pending_notes = getattr(self, '_pending_model_notes', {})
+            _msn = _pending_notes.pop(session_key, None) if session_key else None
+            if _msn:
+                message = _msn + "\n\n" + message
+
             _approval_session_key = session_key or ""
             _approval_session_token = set_current_session_key(_approval_session_key)
             register_gateway_notify(_approval_session_key, _approval_notify_sync)