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- Remove 9 outdated specification docs (v0.2.0 API design)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

@@ -0,0 +1,68 @@
+# Architecture
+
+System design and component overview.
+
+---
+
+## Component Diagram
+
+See README.md for architecture diagram.
+
+---
+
+## Key Components
+
+### FastAPI Server (`api/main.py`)
+- REST API endpoints
+- Request validation
+- Response formatting
+
+### Job Manager (`api/job_manager.py`)
+- Job lifecycle management
+- SQLite operations
+- Concurrency control
+
+### Simulation Worker (`api/simulation_worker.py`)
+- Background job execution
+- Date-sequential, model-parallel orchestration
+- Error handling
+
+### Model-Day Executor (`api/model_day_executor.py`)
+- Single model-day execution
+- Runtime config isolation
+- Agent invocation
+
+### Base Agent (`agent/base_agent/base_agent.py`)
+- Trading session execution
+- MCP tool integration
+- Position management
+
+### MCP Services (`agent_tools/`)
+- Math, Search, Trade, Price tools
+- Internal HTTP servers
+- Localhost-only access
+
+---
+
+## Data Flow
+
+1. API receives trigger request
+2. Job Manager validates and creates job
+3. Worker starts background execution
+4. For each date (sequential):
+   - For each model (parallel):
+     - Executor creates isolated runtime config
+     - Agent executes trading session
+     - Results stored in database
+5. Job status updated
+6. Results available via API
+
+---
+
+## Anti-Look-Ahead Controls
+
+- `TODAY_DATE` in runtime config limits data access
+- Price queries filter by date
+- Search results filtered by publication date
+
+See [CLAUDE.md](../../CLAUDE.md) for implementation details.