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- Remove 9 outdated specification docs (v0.2.0 API design)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/reference/data-formats.md

@@ -0,0 +1,30 @@
+# Data Formats
+
+File formats and schemas used by AI-Trader.
+
+---
+
+## Position File (`position.jsonl`)
+
+```jsonl
+{"date": "2025-01-16", "id": 1, "this_action": {"action": "buy", "symbol": "AAPL", "amount": 10}, "positions": {"AAPL": 10, "CASH": 9500.0}}
+{"date": "2025-01-17", "id": 2, "this_action": {"action": "sell", "symbol": "AAPL", "amount": 5}, "positions": {"AAPL": 5, "CASH": 10750.0}}
+```
+
+---
+
+## Price Data (`merged.jsonl`)
+
+```jsonl
+{"Meta Data": {"2. Symbol": "AAPL", "3. Last Refreshed": "2025-01-16"}, "Time Series (Daily)": {"2025-01-16": {"1. buy price": "250.50", "2. high": "252.00", "3. low": "249.00", "4. sell price": "251.50", "5. volume": "50000000"}}}
+```
+
+---
+
+## Log Files (`log.jsonl`)
+
+Contains complete AI reasoning and tool usage for each trading session.
+
+---
+
+See database schema in [docs/developer/database-schema.md](../developer/database-schema.md) for SQLite formats.