docs: add tutorial links to READMEs

Add prominent links to full tutorials with flow diagrams:
- English README: links to pcircle-ai.github.io/linekit/
- Chinese README: links to pcircle-ai.github.io/linekit/index-zh.html

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

Author: kevintseng

README.md

@@ -87,6 +87,8 @@ if (login.validateState(savedState, returnedState)) {
 
 ## Documentation
 
+📚 **[Full Tutorials & API Reference](https://pcircle-ai.github.io/linekit/)** - Comprehensive guides with flow diagrams
+
 - [User Guide](docs/usage-guide.md): Detailed usage instructions and code examples.
 - [Architecture](docs/architecture.md): System overview and component breakdown.
 - [Design Principles](docs/design-principles.md): Core philosophies behind the toolkit.

README.zh-TW.md

@@ -87,6 +87,8 @@ if (login.validateState(savedState, returnedState)) {
 
 ## 文件
 
+📚 **[完整教學與 API 參考](https://pcircle-ai.github.io/linekit/index-zh.html)** - 附流程圖的詳細指南
+
 - [使用指南](docs/usage-guide.md): 詳細的使用說明和程式碼範例。
 - [架構說明](docs/architecture.md): 系統概觀和元件細節。
 - [設計原則](docs/design-principles.md): 工具包背後的核心理念。