refactor: Enhance GenerationJobManager with In-Memory Implementations

- Introduced InMemoryJobStore, InMemoryEventTransport, and InMemoryContentState for improved job management and event handling.
- Updated GenerationJobManager to utilize these new implementations, allowing for better separation of concerns and easier maintenance.
- Enhanced job metadata handling to support user messages and response IDs for resumable functionality.
- Improved cleanup and state management processes to prevent memory leaks and ensure efficient resource usage.

client/src/hooks/SSE/useResumeOnLoad.ts

@@ -62,7 +62,7 @@ function buildSubmissionFromResumeState(
     content: (resumeState.aggregatedContent as TMessage['content']) ?? [],
     isCreatedByUser: false,
     role: 'assistant',
-    sender: existingResponseMessage?.sender,
+    sender: existingResponseMessage?.sender ?? resumeState.sender,
     model: existingResponseMessage?.model,
   } as TMessage;