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/api/v1/shop/content_pages.py

@@ -7,7 +7,6 @@ No authentication required.
 """
 
 import logging
-from typing import List
 
 from fastapi import APIRouter, Depends, HTTPException, Request
 from pydantic import BaseModel
@@ -52,7 +51,7 @@ class ContentPageListItem(BaseModel):
 # ============================================================================
 
 
-@router.get("/navigation", response_model=List[ContentPageListItem])
+@router.get("/navigation", response_model=list[ContentPageListItem])
 def get_navigation_pages(request: Request, db: Session = Depends(get_db)):
     """
     Get list of content pages for navigation (footer/header).