feat: Complete Flask backend refactoring with comprehensive test suite

- Finalize pytest infrastructure with database mocking
- Enable full test coverage for modular Blueprint architecture
- Prepare foundation for FastAPI + Airflow parallel development
- Support OpenBB Platform (Linux Foundation FINOS member) integration patterns
- Resolve test suite blockers through comprehensive mock data configuration

Author: BorisQuanLi

backend/tests/conftest.py

@@ -43,6 +43,36 @@ def execute_side_effect(query, params=None):
                 mock_cursor.fetchall.return_value = mock_quarterly_reports_data
             elif "select prices_pe.* from prices_pe" in query_lower:
                 mock_cursor.fetchall.return_value = mock_prices_pe_data
+            elif "select distinct(sub_industries.sector_gics)" in query_lower:
+                # Mock sector names query
+                mock_cursor.fetchall.return_value = [('Information Technology',), ('Healthcare',), ('Energy',)]
+            elif "select distinct(sub_industries.sub_industry_gics)" in query_lower:
+                # Mock sub-sector names query
+                mock_cursor.fetchall.return_value = [('Application Software',), ('Systems Software',)]
+            elif "extract(year from date::date) as year" in query_lower and "avg(revenue)" in query_lower:
+                # Mock sector quarterly financials query
+                mock_cursor.fetchall.return_value = [
+                    ('Information Technology', 2023, 4, 1000.0, 200.0, 2.5, 0.20),
+                    ('Information Technology', 2024, 1, 1100.0, 220.0, 2.7, 0.22)
+                ]
+            elif "extract(year from date::date) as year" in query_lower and "avg(closing_price)" in query_lower:
+                # Mock sector price PE query
+                mock_cursor.fetchall.return_value = [
+                    (2023, 4, 150.0, 25.0),
+                    (2024, 1, 160.0, 26.0)
+                ]
+            elif "sub_industry_gics" in query_lower and "avg(revenue)" in query_lower:
+                # Mock sub-sector quarterly financials query
+                mock_cursor.fetchall.return_value = [
+                    ('Application Software', 2023, 4, 1200.0, 240.0, 3.0, 0.25),
+                    ('Application Software', 2024, 1, 1300.0, 260.0, 3.2, 0.27)
+                ]
+            elif "sub_industry_gics" in query_lower and "avg(closing_price)" in query_lower:
+                # Mock sub-sector price PE query
+                mock_cursor.fetchall.return_value = [
+                    ('Application Software', 2023, 4, 180.0, 30.0),
+                    ('Application Software', 2024, 1, 190.0, 31.0)
+                ]
             else:
                 mock_cursor.fetchall.return_value = [] # Default to empty list for unmocked queries