feat: add unified linting scripts and git hooks for code quality enforcement

- Introduced `lint` and `lint-fix` applications in `flake.nix` for unified linting of backend (Python) and frontend (TypeScript/Svelte) code.
- Added `scripts/lint.sh` for manual linting execution.
- Created `scripts/install-hooks.sh` to set up git hooks for automatic linting before commits and optional tests before pushes.
- Updated `README.md` with instructions for using the new linting features and git hooks.

backend/app/auth/schemas.py

@@ -1,6 +1,6 @@
 """Authentication schemas for request/response validation."""
+
 from datetime import datetime
-from typing import Optional
 from uuid import UUID
 
 from pydantic import BaseModel, EmailStr, Field
@@ -42,4 +42,3 @@ class TokenResponse(BaseModel):
     access_token: str
     token_type: str = "bearer"
     user: UserResponse
-