fix(api): Fix S3 backup path-style configuration and improve UX.

- Fix critical S3 client configuration bug for path-style addressing
- Add toast notifications for better user feedback on S3 config operations
- Set up Toaster component in root layout for app-wide notifications
- Clean up unused imports in test files

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude <noreply@anthropic.com>

pyproject.toml

@@ -89,5 +89,5 @@ markers = [
 ]
 
 [[tool.mypy.overrides]]
-module = ["apscheduler.*", "discord_webhook.*"]
+module = ["apscheduler.*", "discord_webhook.*", "botocore.*", "boto3.*"]
 ignore_missing_imports = true