frontend: Fix assistants_web client imports

[tianjing-li]

Removes unneeded default_agent router
Replaces CreateUser schema with correct generated one

AI Description

This PR makes several changes to the backend and frontend code related to agents and routers.

Backend Changes

• src/backend/config/routers.py: The RouterName.DEFAULT_AGENT section has been removed.
• src/backend/routers/agent.py: The default_agent_router has been removed.
• src/backend/routers/chat.py: A line has been removed, likely related to the chat stream function.
• src/backend/schemas/agent.py: The AgentTaskResponse class has been removed, and the from typing import statement has been modified to remove Any, Dict, Optional.
• src/backend/services/agent.py: The TASK_TRACE_PREVIEW_LIMIT constant has been removed.
• src/backend/main.py: The default_agent_router import and its usage in the create_app function have been removed.

Frontend Changes

• src/interfaces/assistants_web/src/app/tasks/[agentId]/page.tsx: The entire file has been removed, which contained a React component for displaying agent tasks.
• src/interfaces/assistants_web/src/cohere-client/client.ts: The createUser method has been updated to use a different request body type, and the getAgentTasks, getDefaultAgent, and createUser methods have been removed.
• src/interfaces/assistants_web/src/cohere-client/generated/services.gen.ts: The HTTPException message has been updated to include the possibility of synthesis failure.
• src/interfaces/assistants_web/src/hooks/use-agents.ts: The useAgentTasks and useDefaultAgent functions have been removed.
• src/interfaces/assistants_web/src/hooks/use-session.ts: The createUser method's parameters have been modified to use a request body object.
• src/interfaces/coral_web/src/cohere-client/client.ts: The getDefaultAgent method has been removed.
• src/interfaces/coral_web/src/cohere-client/generated/services.gen.ts: The getDefaultAgentV1DefaultAgentGet method has been removed.
• src/interfaces/coral_web/src/cohere-client/generated/types.gen.ts: The GetDefaultAgentV1DefaultAgentGetResponse type has been removed.
• src/interfaces/coral_web/src/hooks/agents.ts: The useDefaultAgent function has been removed.

[codecov-commenter]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 79.73%. Comparing base (2900eb0) to head (82ad4f1).
Report is 1 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #820      +/-   ##
==========================================
- Coverage   79.87%   79.73%   -0.15%     
==========================================
  Files         244      244              
  Lines       10436    10486      +50     
==========================================
+ Hits         8336     8361      +25     
- Misses       2100     2125      +25     

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[EugeneLightsOn]

Looks good to me