docs: rewrite README with focus on ADK, simplify style

[shentongmartin]

Summary

Problem	Solution
README was verbose with marketing language	Rewrote in down-to-earth, matter-of-fact style
Quick Start section showed low-level orchestration details	Restructured around ChatModelAgent, DeepAgent, and Composition
Key Features section was too long	Simplified to 4 key capabilities with links
Missing links to examples and docs	Added links to eino-ext, eino-examples, and cloudwego docs

Key Changes

Overview Section

• Simplified introduction, removed marketing phrases
• Added 4 clear bullet points: Components, ADK, Composition, Examples
• Each item now links to relevant repo (eino-ext, eino-examples)

Quick Start Section (completely rewritten)

• ChatModelAgent: Shows how simple it is to get started
• DeepAgent: Shows power of task orchestration for complex problems
• Composition: Shows how to build precise workflows and expose them as tools for agents
• Each section has links to examples and documentation

Key Features Section (simplified from ~60 lines to ~25 lines)

• Component Ecosystem: abstractions + official implementations
• Stream Processing: automatic handling in orchestration
• Callback Aspects: inject logging/tracing/metrics
• Interrupt/Resume: pause for human input, resume from checkpoint

Style Changes

• Removed adjectives without substance
• Chinese README rewritten to sound native, not translated
• Consistent link formatting throughout

Key Insight

The README now tells a clear story: start simple with ChatModelAgent, scale up with DeepAgent for complex tasks, use Composition when you need precise control.

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概要

问题	解决方案
README 冗长，充斥营销用语	改写为朴实、务实的风格
快速上手展示底层编排细节	围绕 ChatModelAgent、DeepAgent、编排重构
主要特性部分过长	精简为 4 个关键能力并附链接
缺少示例和文档链接	添加 eino-ext、eino-examples、cloudwego 文档链接

主要改动

简介部分

• 精简介绍，去掉营销用语
• 4 个清晰要点：组件、ADK、编排、示例
• 每项链接到相关仓库

快速上手部分（完全重写）

• ChatModelAgent：展示上手有多简单
• DeepAgent：展示复杂任务的编排能力
• 编排：展示如何构建精确工作流并作为工具给智能体用

主要特性部分（从约 60 行精简到约 25 行）

• 组件生态：抽象 + 官方实现
• 流式处理：编排中自动处理
• 回调切面：注入日志/追踪/指标
• 中断/恢复：暂停等待人工输入，从检查点恢复

风格改动

• 去掉空洞形容词
• 中文 README 改写为原生中文风格
• 全文链接格式统一

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 81.73%. Comparing base (f2c03c3) to head (75e901d).
⚠️ Report is 3 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #748      +/-   ##
==========================================
- Coverage   81.78%   81.73%   -0.06%     
==========================================
  Files         129      129              
  Lines       12426    12427       +1     
==========================================
- Hits        10163    10157       -6     
- Misses       1509     1516       +7     
  Partials      754      754              

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