feat(docs): Update README Documentation with ADK

[shentongmartin]

Update README Documentation with ADK (Agent Development Kit) Introduction

Summary

This PR updates both English and Chinese README files to reflect the current state of the Eino framework, with a particular focus on introducing the Agent Development Kit (ADK) package—a significant addition that was previously undocumented.

Motivation

The existing README focused primarily on the compose package (Chain, Graph, Workflow) for orchestration but omitted the adk package entirely. This created a gap between the documentation and the actual capabilities of the framework. The ADK represents a higher-level abstraction layer built on top of compose, optimized for building AI agents with less boilerplate—a distinction that needed to be clearly communicated to users.

Key Decisions

1. Organic Integration over Separate Documentation

Rather than creating a separate ADK documentation section, we integrated ADK naturally into the existing document flow. The ReAct agent example—which was previously implemented using raw graph orchestration—now uses ChatModelAgent, demonstrating how ADK simplifies common patterns while the underlying orchestration benefits remain available.

2. Restructured "Quick Walkthrough" Section

• Moved the graph orchestration benefits (type checking, stream processing, etc.) to appear immediately after the Workflow example, keeping orchestration concepts together
• Placed the ReAct/ADK section after orchestration fundamentals, establishing a natural progression from low-level to high-level abstractions

3. Emphasized ADK's Core Strengths

Added concrete examples for:

• Multi-Agent with Context Management: Demonstrating SetSubAgents and NewAgentTool with automatic conversation history rewriting
• Interrupt/Resume: Showing the human-in-the-loop capability with checkpoint persistence
• Prebuilt Patterns: Highlighting Deep Agent (battle-tested), Supervisor, and Sequential patterns
• Middleware System: Illustrating extensibility without core logic modification

4. Consolidated Aspects into Powerful Orchestration

The separate "Highly Extensible Aspects (Callbacks)" section was merged into "Powerful Orchestration" as a bullet point. This reflects that aspects are a feature of the orchestration system rather than a standalone capability.

5. Updated Framework Imagery

Replaced outdated framework structure diagrams with current versions that better represent the project architecture.

Changes

• Added one-line ADK introduction in the overview bullet list
• Restructured ReAct section with ADK ChatModelAgent example
• Added comprehensive ADK capability demonstrations
• Added "Agent Development Kit (ADK)" section under Key Features
• Merged Aspects content into Powerful Orchestration
• Updated framework structure images
• Synchronized all changes between EN and CN READMEs
• Fixed minor inconsistencies (LlamaIndex → Google ADK, variable naming)

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 81.59%. Comparing base (520e4d8) to head (1b07b4c).
⚠️ Report is 5 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #686      +/-   ##
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+ Coverage   81.51%   81.59%   +0.08%     
==========================================
  Files         125      125              
  Lines       12101    12101              
==========================================
+ Hits         9864     9874      +10     
+ Misses       1505     1497       -8     
+ Partials      732      730       -2     

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