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>

app/routes/vendor_pages.py

@@ -22,15 +22,17 @@ Routes:
 """
 
 import logging
-from typing import Optional
 
 from fastapi import APIRouter, Depends, HTTPException, Path, Request
 from fastapi.responses import HTMLResponse, RedirectResponse
 from fastapi.templating import Jinja2Templates
 from sqlalchemy.orm import Session
 
-from app.api.deps import (get_current_vendor_from_cookie_or_header,
-                          get_current_vendor_optional, get_db)
+from app.api.deps import (
+    get_current_vendor_from_cookie_or_header,
+    get_current_vendor_optional,
+    get_db,
+)
 from app.services.content_page_service import content_page_service
 from models.database.user import User
 
@@ -57,7 +59,7 @@ async def vendor_root_no_slash(vendor_code: str = Path(..., description="Vendor
 @router.get("/{vendor_code}/", response_class=RedirectResponse, include_in_schema=False)
 async def vendor_root(
     vendor_code: str = Path(..., description="Vendor code"),
-    current_user: Optional[User] = Depends(get_current_vendor_optional),
+    current_user: User | None = Depends(get_current_vendor_optional),
 ):
     """
     Redirect /vendor/{code}/ based on authentication status.
@@ -78,7 +80,7 @@ async def vendor_root(
 async def vendor_login_page(
     request: Request,
     vendor_code: str = Path(..., description="Vendor code"),
-    current_user: Optional[User] = Depends(get_current_vendor_optional),
+    current_user: User | None = Depends(get_current_vendor_optional),
 ):
     """
     Render vendor login page.
@@ -374,7 +376,7 @@ async def vendor_content_page(
     shadowing other specific routes.
     """
     logger.debug(
-        f"[VENDOR_HANDLER] vendor_content_page REACHED",
+        "[VENDOR_HANDLER] vendor_content_page REACHED",
         extra={
             "path": request.url.path,
             "vendor_code": vendor_code,