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/repository.py

@@ -1,9 +1,7 @@
 """User repository for database operations."""
-from typing import Optional
+
 from uuid import UUID
 
-from sqlalchemy import select
-from sqlalchemy.ext.asyncio import AsyncSession
 from sqlalchemy.orm import Session
 
 from app.auth.security import hash_password
@@ -16,7 +14,7 @@ class UserRepository:
     def __init__(self, db: Session):
         """
         Initialize repository.
-        
+
         Args:
             db: Database session
         """
@@ -25,48 +23,45 @@ class UserRepository:
     def create_user(self, email: str, password: str) -> User:
         """
         Create a new user.
-        
+
         Args:
             email: User email (will be lowercased)
             password: Plain text password (will be hashed)
-            
+
         Returns:
             Created user instance
         """
         email = email.lower()
         password_hash = hash_password(password)
-        
-        user = User(
-            email=email,
-            password_hash=password_hash
-        )
-        
+
+        user = User(email=email, password_hash=password_hash)
+
         self.db.add(user)
         self.db.commit()
         self.db.refresh(user)
-        
+
         return user
 
-    def get_user_by_email(self, email: str) -> Optional[User]:
+    def get_user_by_email(self, email: str) -> User | None:
         """
         Get user by email address.
-        
+
         Args:
             email: User email to search for
-            
+
         Returns:
             User if found, None otherwise
         """
         email = email.lower()
         return self.db.query(User).filter(User.email == email).first()
 
-    def get_user_by_id(self, user_id: UUID) -> Optional[User]:
+    def get_user_by_id(self, user_id: UUID) -> User | None:
         """
         Get user by ID.
-        
+
         Args:
             user_id: User UUID
-            
+
         Returns:
             User if found, None otherwise
         """
@@ -75,13 +70,12 @@ class UserRepository:
     def email_exists(self, email: str) -> bool:
         """
         Check if email already exists.
-        
+
         Args:
             email: Email to check
-            
+
         Returns:
             True if email exists, False otherwise
         """
         email = email.lower()
         return self.db.query(User).filter(User.email == email).first() is not None
-