docs(src): Add comprehensive architecture and agent relationships documentation

- Add overall system architecture with 7-layer visual diagram
- Document component interaction flows (4 detailed workflows)
- Add module dependency graph (5-tier hierarchy)
- Document 9 key integration points between modules
- Add 7 architecture patterns used in the system
- Add comprehensive agent architecture section:
  - DocumentAgent (core with 99-100% accuracy)
  - AIDocumentAgent (AI-enhanced, inherits from DocumentAgent)
  - TagAwareDocumentAgent (adaptive, wraps DocumentAgent)
  - DeepAgent (LangChain-based, independent conversational agent)
- Add agent selection guide with 8 use cases
- Add 4 integration patterns with working code examples
- Include visual diagrams showing agent relationships
- Document dependencies and usage examples for each agent

This provides complete architectural overview showing how all 20 modules
interconnect and how the agent family works together.

Author: vinod0m