IAV-595/feat(agents): Frontend integration for agent management (CRUD + activation logic)

Summary

This MR implements the complete frontend integration for the agent management system, enabling users to manage their main agent and sub-agents through the UI.

Changes

New Features

Feature	Description
Get Main Agent	Retrieve the main agent associated with a user
List Sub-Agents	List all sub-agents with optional active status filter
Add Sub-Agent	Create a new sub-agent under the user's main agent
Rename Sub-Agent	Update the name of an existing sub-agent

Activation/Deactivation Logic

Deactivation Rules

• Main Agent: Deactivating a main agent will automatically deactivate all associated sub-agents (cascade deactivation)
• Sub-Agent: Deactivating a sub-agent only affects that specific agent

Activation Rules

• Main Agent: Can be activated independently without any prerequisites
• Sub-Agent: Can only be activated if the parent main agent is currently active. If the main agent is deactivated, the sub-agent cannot be activated until the main agent is reactivated first.

Testing

• Verify main agent retrieval by user UID
• Verify sub-agents listing with and without active filter
• Test sub-agent creation
• Test sub-agent renaming
• Test main agent deactivation cascades to sub-agents
• Test sub-agent cannot be activated when main agent is inactive
• Test sub-agent activation succeeds when main agent is active

Related Issues

Closes IAV-595