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>

main.py

@@ -18,7 +18,7 @@ if sys.platform == "win32":
     sys.stderr = io.TextIOWrapper(sys.stderr.buffer, encoding="utf-8")
 
 import logging
-from datetime import datetime, timezone
+from datetime import UTC, datetime
 from pathlib import Path
 
 from fastapi import Depends, FastAPI, HTTPException, Request, Response
@@ -35,11 +35,13 @@ from app.core.database import get_db
 from app.core.lifespan import lifespan
 from app.exceptions import ServiceUnavailableException
 from app.exceptions.handler import setup_exception_handlers
+
 # Import page routers
 from app.routes import admin_pages, shop_pages, vendor_pages
 from middleware.context import ContextMiddleware
 from middleware.logging import LoggingMiddleware
 from middleware.theme_context import ThemeContextMiddleware
+
 # Import REFACTORED class-based middleware
 from middleware.vendor_context import VendorContextMiddleware
 
@@ -259,9 +261,8 @@ async def vendor_root_path(
         return templates.TemplateResponse(
             template_path, get_shop_context(request, db=db, page=landing_page)
         )
-    else:
-        # No landing page - redirect to shop
-        return RedirectResponse(url=f"/vendors/{vendor_code}/shop/", status_code=302)
+    # No landing page - redirect to shop
+    return RedirectResponse(url=f"/vendors/{vendor_code}/shop/", status_code=302)
 
 
 # ============================================================================
@@ -317,18 +318,17 @@ async def platform_homepage(request: Request, db: Session = Depends(get_db)):
                 "footer_pages": footer_pages,
             },
         )
-    else:
-        # Fallback to default static template
-        logger.info("[PLATFORM] No CMS homepage found, using default template")
+    # Fallback to default static template
+    logger.info("[PLATFORM] No CMS homepage found, using default template")
 
-        return templates.TemplateResponse(
-            "platform/homepage-default.html",
-            {
-                "request": request,
-                "header_pages": header_pages,
-                "footer_pages": footer_pages,
-            },
-        )
+    return templates.TemplateResponse(
+        "platform/homepage-default.html",
+        {
+            "request": request,
+            "header_pages": header_pages,
+            "footer_pages": footer_pages,
+        },
+    )
 
 
 @app.get("/{slug}", response_class=HTMLResponse, include_in_schema=False)
@@ -349,7 +349,10 @@ async def platform_content_page(
 
     # Load page from CMS
     page = content_page_service.get_page_for_vendor(
-        db, slug=slug, vendor_id=None, include_unpublished=False  # Platform pages only
+        db,
+        slug=slug,
+        vendor_id=None,
+        include_unpublished=False,  # Platform pages only
     )
 
     if not page:
@@ -430,30 +433,27 @@ async def root(request: Request, db: Session = Depends(get_db)):
             return templates.TemplateResponse(
                 template_path, get_shop_context(request, db=db, page=landing_page)
             )
-        else:
-            # No landing page - redirect to shop
-            vendor_context = getattr(request.state, "vendor_context", None)
-            access_method = (
-                vendor_context.get("detection_method", "unknown")
-                if vendor_context
-                else "unknown"
-            )
+        # No landing page - redirect to shop
+        vendor_context = getattr(request.state, "vendor_context", None)
+        access_method = (
+            vendor_context.get("detection_method", "unknown")
+            if vendor_context
+            else "unknown"
+        )
 
-            if access_method == "path":
-                full_prefix = (
-                    vendor_context.get("full_prefix", "/vendor/")
-                    if vendor_context
-                    else "/vendor/"
-                )
-                return RedirectResponse(
-                    url=f"{full_prefix}{vendor.subdomain}/shop/", status_code=302
-                )
-            else:
-                # Domain/subdomain
-                return RedirectResponse(url="/shop/", status_code=302)
-    else:
-        # No vendor - platform root
-        return RedirectResponse(url="/documentation")
+        if access_method == "path":
+            full_prefix = (
+                vendor_context.get("full_prefix", "/vendor/")
+                if vendor_context
+                else "/vendor/"
+            )
+            return RedirectResponse(
+                url=f"{full_prefix}{vendor.subdomain}/shop/", status_code=302
+            )
+        # Domain/subdomain
+        return RedirectResponse(url="/shop/", status_code=302)
+    # No vendor - platform root
+    return RedirectResponse(url="/documentation")
 
 
 @app.get("/health")
@@ -464,7 +464,7 @@ def health_check(db: Session = Depends(get_db)):
         db.execute(text("SELECT 1"))
         return {
             "status": "healthy",
-            "timestamp": datetime.now(timezone.utc),
+            "timestamp": datetime.now(UTC),
             "message": f"{settings.project_name} v{settings.version}",
             "docs": {
                 "swagger": "/docs",