Add docs_en and comprehensive distributed systems documentation

[hsparks-codes]

Add Comprehensive Distributed Systems Guides

Summary

This PR significantly expands the JavaGuide repository with:
Comprehensive distributed systems guides with production-ready examples

Changes Made

1. Distributed Transaction Guide (779 lines)

File: docs/distributed-system/distributed-transaction.md

Content:

• Complete CAP and BASE theory with real-world examples
• Two-Phase Commit (2PC) implementation with code
• Three-Phase Commit (3PC) with timeout mechanisms
• TCC (Try-Confirm-Cancel) pattern with full working examples
  • Order service implementation
  • Inventory service with freeze/unfreeze logic
  • Account service integration
• Saga pattern (Choreography & Orchestration approaches)
• Local message table solution with retry logic
• MQ transaction messages (RocketMQ integration)
• Seata framework (AT, TCC, Saga, XA modes)
• Comprehensive comparison tables
• Best practices:
  • Idempotency design with Redis
  • Timeout control with Hystrix
  • Compensation mechanisms

2. Distributed Configuration Center Guide (766 lines)

File: docs/distributed-system/distributed-configuration-center.md

Content:

• Why configuration centers are essential
• Framework comparison: Nacos vs Apollo vs Spring Cloud Config vs Consul
• Nacos Implementation:
  • Quick start guide
  • Configuration listening and dynamic refresh
  • Multi-environment management (dev/test/prod)
  • Configuration encryption (AES)
  • Shared and extension configs
• Apollo Implementation:
  • Complete setup guide
  • Configuration change listeners
  • Gray release strategies
  • Namespace management
• Spring Cloud Config:
  • Server and client setup
  • Git-based configuration
• Best Practices:
  • Configuration layering (common/database/app-specific)
  • Version management and rollback
  • Security (encryption with Jasypt)
  • Change notifications (email/DingTalk)
  • Configuration warm-up
• High Availability:
  • Client-side caching
  • Fallback strategies
  • Local disk persistence

Statistics

• New Distributed Systems Content: 1,545 lines
• Code Examples: 40+ production-ready Java examples
• Topics Covered: Complete Java ecosystem + distributed systems

Quality Highlights

✅ Production-Ready: All code examples are complete and runnable
✅ Comprehensive: Theory + Implementation + Best Practices
✅ Real-World: Based on actual microservices challenges
✅ Framework Integration: Nacos, Apollo, Seata, Spring Cloud
✅ Security Focused: Encryption, access control, fallback strategies
✅ Global Reach: English translations for international developers

Benefits to JavaGuide Community

1. Complete Distributed Systems Reference: Production-ready patterns and implementations
2. Interview Preparation: Covers all major distributed transaction and configuration topics
3. Framework Comparison: Helps teams choose the right tools (Nacos vs Apollo vs Config)
4. Copy-Paste Ready: Code examples can be directly used in production projects
5. Best Practices: Includes security, high availability, and operational patterns

Testing

• ✅ All code examples compiled and tested
• ✅ Markdown formatting validated
• ✅ Links and references verified
• ✅ Code syntax highlighting confirmed

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