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>

tasks/marketplace_import.py

@@ -1,7 +1,7 @@
 # Marketplace CSV import tasks
 # app/tasks/background_tasks.py
 import logging
-from datetime import datetime, timezone
+from datetime import UTC, datetime
 
 from app.core.database import SessionLocal
 from app.utils.csv_processor import CSVProcessor
@@ -40,13 +40,13 @@ async def process_marketplace_import(
             logger.error(f"Vendor {vendor_id} not found for import job {job_id}")
             job.status = "failed"
             job.error_message = f"Vendor {vendor_id} not found"
-            job.completed_at = datetime.now(timezone.utc)
+            job.completed_at = datetime.now(UTC)
             db.commit()
             return
 
         # Update job status
         job.status = "processing"
-        job.started_at = datetime.now(timezone.utc)
+        job.started_at = datetime.now(UTC)
         db.commit()
 
         logger.info(
@@ -65,7 +65,7 @@ async def process_marketplace_import(
 
         # Update job with results
         job.status = "completed"
-        job.completed_at = datetime.now(timezone.utc)
+        job.completed_at = datetime.now(UTC)
         job.imported_count = result["imported"]
         job.updated_count = result["updated"]
         job.error_count = result.get("errors", 0)
@@ -88,13 +88,13 @@ async def process_marketplace_import(
             try:
                 job.status = "failed"
                 job.error_message = str(e)
-                job.completed_at = datetime.now(timezone.utc)
+                job.completed_at = datetime.now(UTC)
                 db.commit()
             except Exception as commit_error:
                 logger.error(f"Failed to update job status: {commit_error}")
                 db.rollback()
     finally:
-        if hasattr(db, "close") and callable(getattr(db, "close")):
+        if hasattr(db, "close") and callable(db.close):
             try:
                 db.close()
             except Exception as close_error: