refactor: split monolithic app.py into modular Flask application with factory pattern

- Created app/ package with 6 modules:
  - __init__.py: Application factory (create_app function)
  - routes.py: All route handlers (473 lines)
  - models.py: Data persistence layer (41 lines)
  - validators.py: Input validation functions (48 lines)
  - email_service.py: Email sending functions (85 lines)
  - utils.py: Utility functions (30 lines)

- Implemented Flask application factory pattern
- Created run.py as minimal entry point
- Updated all test imports to use new module structure
- Fixed template/static folder paths for package structure

- All 102 tests passing
- Improved maintainability with clear separation of concerns
- Follows Flask best practices for scalable applications

tests/test_config.py

@@ -4,7 +4,7 @@ Tests for configuration settings and helper functions.
 import pytest
 import os
 from config import Config
-from app import get_application_path, get_data_file_path, get_attachments_path
+from app.models import get_application_path, get_data_file_path, get_attachments_path
 
 
 class TestConfiguration:
@@ -59,33 +59,37 @@ class TestPathHelpers:
 
     def test_get_application_path(self, app):
         """Test get_application_path returns correct path."""
-        session_id = 'test-123'
-        expected_path = os.path.join(app.config['APPLICATIONS_FOLDER'], session_id)
-        assert get_application_path(session_id) == expected_path
+        with app.app_context():
+            session_id = 'test-123'
+            expected_path = os.path.join(app.config['APPLICATIONS_FOLDER'], session_id)
+            assert get_application_path(session_id) == expected_path
 
     def test_get_data_file_path(self, app):
         """Test get_data_file_path returns correct YAML file path."""
-        session_id = 'test-456'
-        expected_path = os.path.join(
-            app.config['APPLICATIONS_FOLDER'],
-            session_id,
-            'data.yaml'
-        )
-        assert get_data_file_path(session_id) == expected_path
+        with app.app_context():
+            session_id = 'test-456'
+            expected_path = os.path.join(
+                app.config['APPLICATIONS_FOLDER'],
+                session_id,
+                'data.yaml'
+            )
+            assert get_data_file_path(session_id) == expected_path
 
     def test_get_attachments_path(self, app):
         """Test get_attachments_path returns correct attachments directory path."""
-        session_id = 'test-789'
-        expected_path = os.path.join(
-            app.config['APPLICATIONS_FOLDER'],
-            session_id,
-            'attachments'
-        )
-        assert get_attachments_path(session_id) == expected_path
+        with app.app_context():
+            session_id = 'test-789'
+            expected_path = os.path.join(
+                app.config['APPLICATIONS_FOLDER'],
+                session_id,
+                'attachments'
+            )
+            assert get_attachments_path(session_id) == expected_path
 
     def test_path_helpers_with_special_characters(self, app):
         """Test path helpers handle session IDs with special characters."""
-        session_id = 'test-abc-123-def'
-        app_path = get_application_path(session_id)
-        assert session_id in app_path
-        assert os.path.isabs(app_path) or app_path.startswith('.')
+        with app.app_context():
+            session_id = 'test-abc-123-def'
+            app_path = get_application_path(session_id)
+            assert session_id in app_path
+            assert os.path.isabs(app_path) or app_path.startswith('.')