feat: introduce agent orchestrator to bridge agents and backend server

[vcfgv]

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[Copilot]

Pull Request Overview

This PR introduces an agent orchestrator system that provides a unified interface for coordinating interactions between agents and the backend server. The orchestrator manages session and task lifecycle, handles both local and remote agent communication, and provides streaming responses for real-time interaction.

Key changes include:

• Introduces comprehensive type system with unified data models for user input, agents, and responses
• Implements session and task management with in-memory storage
• Creates agent orchestrator with execution planning and streaming capabilities

Reviewed Changes

Copilot reviewed 27 out of 28 changed files in this pull request and generated 3 comments.

Show a summary per file

File	Description
python/valuecell/core/types.py	Defines unified type system with user input models, agent abstractions, and response types
python/valuecell/core/task/*.py	Implements task management with models, storage, and lifecycle operations
python/valuecell/core/session/*.py	Provides session management with message handling and storage
python/valuecell/core/coordinate/*.py	Creates orchestrator system with execution planning and agent coordination
python/valuecell/core/agent/*.py	Updates agent system to use unified types and enhanced connection management
python/valuecell/agents/*.py	Updates existing agents to use new type system

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