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>

scripts/route_diagnostics.py

@@ -6,8 +6,6 @@ Run this script to check if your vendor routes are properly configured.
 Usage: python route_diagnostics.py
 """
 
-import sys
-from typing import Dict, List
 
 
 def check_route_order():
@@ -58,7 +56,7 @@ def check_route_order():
         vendor_info_found = False
         for route in routes:
             if hasattr(route, "path"):
-                if "/{vendor_code}" == route.path and "GET" in getattr(
+                if route.path == "/{vendor_code}" and "GET" in getattr(
                     route, "methods", set()
                 ):
                     vendor_info_found = True
@@ -109,14 +107,13 @@ def test_vendor_endpoint():
             print(f"   Vendor: {data.get('name', 'N/A')}")
             print(f"   Code: {data.get('vendor_code', 'N/A')}")
             return True
-        elif "text/html" in content_type:
+        if "text/html" in content_type:
             print("❌ ERROR: Response is HTML, not JSON!")
             print("   This confirms the route ordering issue")
             print("   The HTML page route is catching the API request")
             return False
-        else:
-            print(f"⚠️  Unknown content type: {content_type}")
-            return False
+        print(f"⚠️  Unknown content type: {content_type}")
+        return False
 
     except requests.exceptions.ConnectionError:
         print("⚠️  Cannot connect to server. Is FastAPI running on localhost:8000?")