* chore: update @librechat/agents dependency to version 3.0.18
* refactor: add optional metadata field to message schema and types
* chore: update @librechat/agents to v3.0.19
* refactor: update return type of sendCompletion method to include metadata
* chore: linting
* chore: update @librechat/agents dependency to v3.0.20
* refactor: implement agent labeling for conversation history in multi-agent scenarios
* refactor: improve error handling for capturing agent ID map in AgentClient
* refactor: clear agentIdMap and related properties during client disposal to prevent memory leaks
* chore: update sendCompletion method for FakeClient to return an object with completion and metadata fields