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/admin_pages.py

@@ -30,15 +30,17 @@ Routes:
 - GET /code-quality/violations/{violation_id} → Violation details (auth required)
 """
 
-from typing import Optional
 
 from fastapi import APIRouter, Depends, 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_admin_from_cookie_or_header,
-                          get_current_admin_optional, get_db)
+from app.api.deps import (
+    get_current_admin_from_cookie_or_header,
+    get_current_admin_optional,
+    get_db,
+)
 from models.database.user import User
 
 router = APIRouter()
@@ -52,7 +54,7 @@ templates = Jinja2Templates(directory="app/templates")
 
 @router.get("/", response_class=RedirectResponse, include_in_schema=False)
 async def admin_root(
-    current_user: Optional[User] = Depends(get_current_admin_optional),
+    current_user: User | None = Depends(get_current_admin_optional),
 ):
     """
     Redirect /admin/ based on authentication status.
@@ -69,7 +71,7 @@ async def admin_root(
 
 @router.get("/login", response_class=HTMLResponse, include_in_schema=False)
 async def admin_login_page(
-    request: Request, current_user: Optional[User] = Depends(get_current_admin_optional)
+    request: Request, current_user: User | None = Depends(get_current_admin_optional)
 ):
     """
     Render admin login page.