feat: add new day-centric results API endpoint

Implements new /results endpoint with day-centric data structure:
- Returns starting_position, daily_metrics, trades, and final_position
- Supports reasoning levels: none (default), summary, full
- Uses database helper methods from trading_days schema
- Replaces old positions-based endpoint

Changes:
- Created api/routes/results_v2.py with new endpoint
- Registered router in api/main.py
- Removed old /results endpoint (positions table)
- Added comprehensive integration tests

All tests pass.

tests/integration/test_results_api_v2.py

@@ -0,0 +1,137 @@
+import pytest
+from fastapi.testclient import TestClient
+from api.main import create_app
+from api.database import Database
+from api.routes.results_v2 import get_database
+
+
+class TestResultsAPIV2:
+
+    @pytest.fixture
+    def client(self, db):
+        """Create test client with overridden database dependency."""
+        # Create fresh app instance
+        app = create_app()
+        # Override the database dependency
+        app.dependency_overrides[get_database] = lambda: db
+        client = TestClient(app)
+        yield client
+        # Clean up
+        app.dependency_overrides.clear()
+
+    @pytest.fixture
+    def db(self, tmp_path):
+        """Create test database with sample data."""
+        import importlib
+        migration_module = importlib.import_module('api.migrations.001_trading_days_schema')
+        create_trading_days_schema = migration_module.create_trading_days_schema
+
+        db_path = tmp_path / "test.db"
+        db = Database(str(db_path))
+
+        # Create schema
+        db.connection.execute("""
+            CREATE TABLE IF NOT EXISTS jobs (
+                job_id TEXT PRIMARY KEY,
+                status TEXT
+            )
+        """)
+        create_trading_days_schema(db)
+
+        # Insert sample data
+        db.connection.execute(
+            "INSERT INTO jobs (job_id, status) VALUES (?, ?)",
+            ("test-job", "completed")
+        )
+
+        # Day 1
+        day1_id = db.create_trading_day(
+            job_id="test-job",
+            model="gpt-4",
+            date="2025-01-15",
+            starting_cash=10000.0,
+            starting_portfolio_value=10000.0,
+            daily_profit=0.0,
+            daily_return_pct=0.0,
+            ending_cash=8500.0,
+            ending_portfolio_value=10000.0,
+            reasoning_summary="First day summary",
+            total_actions=1
+        )
+        db.create_holding(day1_id, "AAPL", 10)
+        db.create_action(day1_id, "buy", "AAPL", 10, 150.0)
+
+        db.connection.commit()
+        return db
+
+    def test_results_without_reasoning(self, client, db):
+        """Test default response excludes reasoning."""
+        response = client.get("/results?job_id=test-job")
+
+        assert response.status_code == 200
+        data = response.json()
+
+        assert data["count"] == 1
+        assert data["results"][0]["reasoning"] is None
+
+    def test_results_with_summary(self, client, db):
+        """Test including reasoning summary."""
+        response = client.get("/results?job_id=test-job&reasoning=summary")
+
+        data = response.json()
+        result = data["results"][0]
+
+        assert result["reasoning"] == "First day summary"
+
+    def test_results_structure(self, client, db):
+        """Test complete response structure."""
+        response = client.get("/results?job_id=test-job")
+
+        result = response.json()["results"][0]
+
+        # Basic fields
+        assert result["date"] == "2025-01-15"
+        assert result["model"] == "gpt-4"
+        assert result["job_id"] == "test-job"
+
+        # Starting position
+        assert "starting_position" in result
+        assert result["starting_position"]["cash"] == 10000.0
+        assert result["starting_position"]["portfolio_value"] == 10000.0
+        assert result["starting_position"]["holdings"] == []  # First day
+
+        # Daily metrics
+        assert "daily_metrics" in result
+        assert result["daily_metrics"]["profit"] == 0.0
+        assert result["daily_metrics"]["return_pct"] == 0.0
+
+        # Trades
+        assert "trades" in result
+        assert len(result["trades"]) == 1
+        assert result["trades"][0]["action_type"] == "buy"
+        assert result["trades"][0]["symbol"] == "AAPL"
+
+        # Final position
+        assert "final_position" in result
+        assert result["final_position"]["cash"] == 8500.0
+        assert result["final_position"]["portfolio_value"] == 10000.0
+        assert len(result["final_position"]["holdings"]) == 1
+        assert result["final_position"]["holdings"][0]["symbol"] == "AAPL"
+
+        # Metadata
+        assert "metadata" in result
+        assert result["metadata"]["total_actions"] == 1
+
+    def test_results_filtering_by_date(self, client, db):
+        """Test filtering results by date."""
+        response = client.get("/results?date=2025-01-15")
+
+        results = response.json()["results"]
+        assert all(r["date"] == "2025-01-15" for r in results)
+
+    def test_results_filtering_by_model(self, client, db):
+        """Test filtering results by model."""
+        response = client.get("/results?model=gpt-4")
+
+        results = response.json()["results"]
+        assert all(r["model"] == "gpt-4" for r in results)