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- Remove 9 outdated specification docs (v0.2.0 API design)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/database-schema.md

@@ -0,0 +1,94 @@
+# Database Schema
+
+SQLite database schema reference.
+
+---
+
+## Tables
+
+### jobs
+Job metadata and overall status.
+
+```sql
+CREATE TABLE jobs (
+    job_id TEXT PRIMARY KEY,
+    config_path TEXT NOT NULL,
+    status TEXT CHECK(status IN ('pending', 'running', 'completed', 'partial', 'failed')),
+    date_range TEXT,  -- JSON array
+    models TEXT,      -- JSON array
+    created_at TEXT,
+    started_at TEXT,
+    completed_at TEXT,
+    total_duration_seconds REAL,
+    error TEXT
+);
+```
+
+### job_details
+Per model-day execution details.
+
+```sql
+CREATE TABLE job_details (
+    id INTEGER PRIMARY KEY AUTOINCREMENT,
+    job_id TEXT,
+    model_signature TEXT,
+    trading_date TEXT,
+    status TEXT CHECK(status IN ('pending', 'running', 'completed', 'failed')),
+    start_time TEXT,
+    end_time TEXT,
+    duration_seconds REAL,
+    error TEXT,
+    FOREIGN KEY (job_id) REFERENCES jobs(job_id) ON DELETE CASCADE
+);
+```
+
+### positions
+Trading position records with P&L.
+
+```sql
+CREATE TABLE positions (
+    id INTEGER PRIMARY KEY AUTOINCREMENT,
+    job_id TEXT,
+    date TEXT,
+    model TEXT,
+    action_id INTEGER,
+    action_type TEXT,
+    symbol TEXT,
+    amount INTEGER,
+    price REAL,
+    cash REAL,
+    portfolio_value REAL,
+    daily_profit REAL,
+    daily_return_pct REAL,
+    created_at TEXT
+);
+```
+
+### holdings
+Portfolio holdings breakdown per position.
+
+```sql
+CREATE TABLE holdings (
+    id INTEGER PRIMARY KEY AUTOINCREMENT,
+    position_id INTEGER,
+    symbol TEXT,
+    quantity REAL,
+    FOREIGN KEY (position_id) REFERENCES positions(id) ON DELETE CASCADE
+);
+```
+
+### price_data
+Cached historical price data.
+
+### price_coverage
+Data availability tracking per symbol.
+
+### reasoning_logs
+AI decision reasoning (when enabled).
+
+### tool_usage
+MCP tool usage statistics.
+
+---
+
+See `api/database.py` for complete schema definitions.