docs: create consolidated developer guides (architecture, development-setup, api-reference)

Phase 2 (Consolidation) - Developer Guide Section Complete

Created 3 comprehensive developer guides:

1. architecture.md (850+ lines)
   - Consolidated: src/README.md, system_overview.md, PHASE2_IMPLEMENTATION_PLAN.md, PHASE2_TASK5_COMPLETE.md
   - 7-layer architecture with ASCII diagrams
   - Component details for all layers (Agent, Parser, LLM, Skill, Memory, Retrieval, Infrastructure)
   - Complete data flow examples (2 workflows with 10-11 steps)
   - 5 design patterns with code examples (Factory, Strategy, Pipeline, Observer, Singleton)
   - Quality attributes and extension guide

2. development-setup.md (700+ lines)
   - Consolidated: building.md, submitting_code.md, PHASE2 docs, setup snippets
   - Complete environment setup (venv, conda, pyenv)
   - LLM provider configuration (Ollama + cloud providers)
   - IDE setup (VS Code with extensions/settings, PyCharm)
   - Pre-commit hooks, testing setup, code quality tools
   - Branch strategy (dev/<alias>/<feature>) and Git2Git workflow
   - Troubleshooting section with 9 common issues
   - Complete checklists (4 categories)

3. api-reference.md (500+ lines)
   - Complete API documentation for public classes
   - DocumentAgent API (5 methods with examples)
   - DocumentParser API (3 methods with examples)
   - LLMRouter API (2 methods with examples)
   - Configuration API utilities
   - Quality metrics structures
   - Type hints and error handling
   - Cross-reference to user guides

Total: 2,050+ lines of developer documentation
Progress: Developer guides 100% complete

Author: vinod0m