test: improve test coverage from 61% to 84.81%

Major improvements:
- Fixed all 42 broken tests (database connection leaks)
- Added db_connection() context manager for proper cleanup
- Created comprehensive test suites for undertested modules

New test coverage:
- tools/general_tools.py: 26 tests (97% coverage)
- tools/price_tools.py: 11 tests (validates NASDAQ symbols, date handling)
- api/price_data_manager.py: 12 tests (85% coverage)
- api/routes/results_v2.py: 3 tests (98% coverage)
- agent/reasoning_summarizer.py: 2 tests (87% coverage)
- api/routes/period_metrics.py: 2 edge case tests (100% coverage)
- agent/mock_provider: 1 test (100% coverage)

Database fixes:
- Added db_connection() context manager to prevent leaks
- Updated 16+ test files to use context managers
- Fixed drop_all_tables() to match new schema
- Added CHECK constraint for action_type
- Added ON DELETE CASCADE to trading_days foreign key

Test improvements:
- Updated SQL INSERT statements with all required fields
- Fixed date parameter handling in API integration tests
- Added edge case tests for validation functions
- Fixed import errors across test suite

Results:
- Total coverage: 84.81% (was 61%)
- Tests passing: 406 (was 364 with 42 failures)
- Total lines covered: 6364 of 7504

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude <noreply@anthropic.com>

tests/api/test_results_v2.py

@@ -46,11 +46,17 @@ def test_validate_both_dates():
 
 
 def test_validate_invalid_date_format():
-    """Test error on invalid date format."""
+    """Test error on invalid start_date format."""
     with pytest.raises(ValueError, match="Invalid date format"):
         validate_and_resolve_dates("2025-1-16", "2025-01-20")
 
 
+def test_validate_invalid_end_date_format():
+    """Test error on invalid end_date format."""
+    with pytest.raises(ValueError, match="Invalid date format"):
+        validate_and_resolve_dates("2025-01-16", "2025-1-20")
+
+
 def test_validate_start_after_end():
     """Test error when start_date > end_date."""
     with pytest.raises(ValueError, match="start_date must be <= end_date"):
@@ -220,3 +226,46 @@ def test_get_results_empty_404(test_db):
 
     assert response.status_code == 404
     assert "No trading data found" in response.json()["detail"]
+
+
+def test_deprecated_date_parameter(test_db):
+    """Test that deprecated 'date' parameter returns 422 error."""
+    app = create_app(db_path=test_db.db_path)
+    app.state.test_mode = True
+
+    # Override the database dependency to use our test database
+    from api.routes.results_v2 import get_database
+
+    def override_get_database():
+        return test_db
+
+    app.dependency_overrides[get_database] = override_get_database
+
+    client = TestClient(app)
+
+    response = client.get("/results?date=2024-01-16")
+
+    assert response.status_code == 422
+    assert "removed" in response.json()["detail"]
+    assert "start_date" in response.json()["detail"]
+
+
+def test_invalid_date_returns_400(test_db):
+    """Test that invalid date format returns 400 error via API."""
+    app = create_app(db_path=test_db.db_path)
+    app.state.test_mode = True
+
+    # Override the database dependency to use our test database
+    from api.routes.results_v2 import get_database
+
+    def override_get_database():
+        return test_db
+
+    app.dependency_overrides[get_database] = override_get_database
+
+    client = TestClient(app)
+
+    response = client.get("/results?start_date=2024-1-16&end_date=2024-01-20")
+
+    assert response.status_code == 400
+    assert "Invalid date format" in response.json()["detail"]