refactor: modernize code quality tooling with Ruff

- Replace black, isort, and flake8 with Ruff (all-in-one linter and formatter)
- Add comprehensive pyproject.toml configuration
- Simplify Makefile code quality targets
- Configure exclusions for venv/.venv in pyproject.toml
- Auto-fix 1,359 linting issues across codebase

Benefits:
- Much faster builds (Ruff is written in Rust)
- Single tool replaces multiple tools
- More comprehensive rule set (UP, B, C4, SIM, PIE, RET, Q)
- All configuration centralized in pyproject.toml
- Better import sorting and formatting consistency

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

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

tests/integration/tasks/test_background_tasks.py

@@ -1,5 +1,4 @@
 # tests/test_background_tasks.py
-from datetime import datetime
 from unittest.mock import AsyncMock, patch
 
 import pytest
@@ -32,8 +31,9 @@ class TestBackgroundTasks:
         job_id = job.id
 
         # Mock CSV processor and prevent session from closing
-        with patch("app.tasks.background_tasks.CSVProcessor") as mock_processor, patch(
-            "app.tasks.background_tasks.SessionLocal", return_value=db
+        with (
+            patch("app.tasks.background_tasks.CSVProcessor") as mock_processor,
+            patch("app.tasks.background_tasks.SessionLocal", return_value=db),
         ):
             mock_instance = mock_processor.return_value
             mock_instance.process_marketplace_csv_from_url = AsyncMock(
@@ -86,10 +86,10 @@ class TestBackgroundTasks:
         job_id = job.id
 
         # Mock CSV processor to raise exception
-        with patch("app.tasks.background_tasks.CSVProcessor") as mock_processor, patch(
-            "app.tasks.background_tasks.SessionLocal", return_value=db
+        with (
+            patch("app.tasks.background_tasks.CSVProcessor") as mock_processor,
+            patch("app.tasks.background_tasks.SessionLocal", return_value=db),
         ):
-
             mock_instance = mock_processor.return_value
             mock_instance.process_marketplace_csv_from_url = AsyncMock(
                 side_effect=Exception("Import failed")
@@ -124,8 +124,9 @@ class TestBackgroundTasks:
     @pytest.mark.asyncio
     async def test_marketplace_import_job_not_found(self, db):
         """Test handling when import job doesn't exist"""
-        with patch("app.tasks.background_tasks.CSVProcessor") as mock_processor, patch(
-            "app.tasks.background_tasks.SessionLocal", return_value=db
+        with (
+            patch("app.tasks.background_tasks.CSVProcessor") as mock_processor,
+            patch("app.tasks.background_tasks.SessionLocal", return_value=db),
         ):
             mock_instance = mock_processor.return_value
             mock_instance.process_marketplace_csv_from_url = AsyncMock(
@@ -170,8 +171,9 @@ class TestBackgroundTasks:
         job_id = job.id
 
         # Mock CSV processor with some errors
-        with patch("app.tasks.background_tasks.CSVProcessor") as mock_processor, patch(
-            "app.tasks.background_tasks.SessionLocal", return_value=db
+        with (
+            patch("app.tasks.background_tasks.CSVProcessor") as mock_processor,
+            patch("app.tasks.background_tasks.SessionLocal", return_value=db),
         ):
             mock_instance = mock_processor.return_value
             mock_instance.process_marketplace_csv_from_url = AsyncMock(