docs: restructure documentation for improved clarity and navigation

Reorganize documentation into user-focused, developer-focused, and deployment-focused sections.

**New structure:**
- Root: README.md (streamlined), QUICK_START.md, API_REFERENCE.md
- docs/user-guide/: configuration, API usage, integrations, troubleshooting
- docs/developer/: contributing, development setup, testing, architecture
- docs/deployment/: Docker deployment, production checklist, monitoring
- docs/reference/: environment variables, MCP tools, data formats

**Changes:**
- Streamline README.md from 831 to 469 lines
- Create QUICK_START.md for 5-minute onboarding
- Create API_REFERENCE.md as single source of truth for API
- Remove 9 outdated specification docs (v0.2.0 API design)
- Remove DOCKER_API.md (content consolidated into new structure)
- Remove docs/plans/ directory with old design documents
- Update CLAUDE.md with documentation structure guide
- Remove orchestration-specific references

**Benefits:**
- Clear entry points for different audiences
- No content duplication
- Better discoverability through logical hierarchy
- All content reflects current v0.3.0 API

docs/developer/testing.md

@@ -0,0 +1,64 @@
+# Testing Guide
+
+Guide for testing AI-Trader during development.
+
+---
+
+## Automated Testing
+
+### Docker Build Validation
+
+```bash
+chmod +x scripts/*.sh
+bash scripts/validate_docker_build.sh
+```
+
+Validates:
+- Docker installation
+- Environment configuration
+- Image build
+- Container startup
+- Health endpoint
+
+### API Endpoint Testing
+
+```bash
+bash scripts/test_api_endpoints.sh
+```
+
+Tests all API endpoints with real simulations.
+
+---
+
+## Unit Tests
+
+```bash
+# Install dependencies
+pip install -r requirements.txt
+
+# Run tests
+pytest tests/ -v
+
+# With coverage
+pytest tests/ -v --cov=api --cov-report=term-missing
+
+# Specific test file
+pytest tests/unit/test_job_manager.py -v
+```
+
+---
+
+##  Integration Tests
+
+```bash
+# Run integration tests only
+pytest tests/integration/ -v
+
+# Test with real API server
+docker-compose up -d
+pytest tests/integration/test_api_endpoints.py -v
+```
+
+---
+
+For detailed testing procedures, see root [TESTING_GUIDE.md](../../TESTING_GUIDE.md).