feat: transform to REST API service with SQLite persistence (v0.3.0)

Major architecture transformation from batch-only to API service with
database persistence for Windmill integration.

## REST API Implementation
- POST /simulate/trigger - Start simulation jobs
- GET /simulate/status/{job_id} - Monitor job progress
- GET /results - Query results with filters (job_id, date, model)
- GET /health - Service health checks

## Database Layer
- SQLite persistence with 6 tables (jobs, job_details, positions,
  holdings, reasoning_logs, tool_usage)
- Foreign key constraints with cascade deletes
- Replaces JSONL file storage

## Backend Components
- JobManager: Job lifecycle management with concurrency control
- RuntimeConfigManager: Thread-safe isolated runtime configs
- ModelDayExecutor: Single model-day execution engine
- SimulationWorker: Date-sequential, model-parallel orchestration

## Testing
- 102 unit and integration tests (85% coverage)
- Database: 98% coverage
- Job manager: 98% coverage
- API endpoints: 81% coverage
- Pydantic models: 100% coverage
- TDD approach throughout

## Docker Deployment
- Dual-mode: API server (persistent) + batch (one-time)
- Health checks with 30s interval
- Volume persistence for database and logs
- Separate entrypoints for each mode

## Validation Tools
- scripts/validate_docker_build.sh - Build validation
- scripts/test_api_endpoints.sh - Complete API testing
- scripts/test_batch_mode.sh - Batch mode validation
- DOCKER_API.md - Deployment guide
- TESTING_GUIDE.md - Testing procedures

## Configuration
- API_PORT environment variable (default: 8080)
- Backwards compatible with existing configs
- FastAPI, uvicorn, pydantic>=2.0 dependencies

Co-Authored-By: AI Assistant <noreply@example.com>

pytest.ini

@@ -0,0 +1,45 @@
+[pytest]
+# Test discovery
+python_files = test_*.py
+python_classes = Test*
+python_functions = test_*
+
+# Output options
+addopts =
+    -v
+    --strict-markers
+    --tb=short
+    --cov=api
+    --cov-report=term-missing
+    --cov-report=html:htmlcov
+    --cov-fail-under=85
+
+# Markers
+markers =
+    unit: Unit tests (fast, isolated)
+    integration: Integration tests (with real dependencies)
+    performance: Performance and benchmark tests
+    security: Security tests
+    e2e: End-to-end tests (Docker required)
+    slow: Tests that take >10 seconds
+
+# Test paths
+testpaths = tests
+
+# Coverage options
+[coverage:run]
+source = api
+omit =
+    */tests/*
+    */conftest.py
+    */__init__.py
+
+[coverage:report]
+exclude_lines =
+    pragma: no cover
+    def __repr__
+    raise AssertionError
+    raise NotImplementedError
+    if __name__ == .__main__.:
+    if TYPE_CHECKING:
+    @abstractmethod