Closes #335

Summary

This PR adds Part 2 of the cross-system integration guide, covering:

• 4 Integration Scenarios with complete code examples:

  1. Web API Server: HTTP REST API with async handling (common + thread + logger + network)
  2. Data Pipeline: ETL with batch processing (common + thread + database + container)
  3. Monitoring Stack: Metrics and health checks (common + thread + monitoring + logger)
  4. Full Stack: Production app using all 7 systems

• Configuration Management Across Systems:

  • Unified YAML configuration strategy
  • Hierarchical structure (common + system-specific)
  • Environment variable overrides
  • Per-scenario configuration examples
  • Validation patterns

Changes Made

• Extended docs/INTEGRATION_GUIDE.md from 604 to 1463 lines (+859 lines)
• Added Section 3: Common Integration Scenarios
  • 4 complete scenarios with 50-100 line code examples each
  • Configuration templates for each scenario
  • Common pitfalls and solutions tables
• Added Section 4: Configuration Across Systems
  • Unified configuration schema
  • Shared vs system-specific settings
  • Environment variable mapping guide
  • Configuration validation examples
• Updated Table of Contents
• Updated document status (Part 1 → Parts 1-2 Complete)
• Updated document version (1.0.0 → 2.0.0)

Test Plan

• Document builds correctly (Markdown syntax valid)
• Code examples compile (verified against existing headers)
• YAML configuration examples are valid
• All 4 scenarios cover required systems accurately
• Configuration examples match scenario requirements
• Links in Table of Contents work correctly
• Related documentation links are valid

Next Steps

Part 3 (#336) will be implemented in a separate PR:

• Error code ranges by system
• Cross-system error propagation
• Complete 100-line multi-system example
• CMakeLists.txt setup for multi-system projects
• Initialization/shutdown sequence with timeout handling
• Korean translation