refactor: fix linting issues and code quality

- Fix import ordering in __init__.py
- Remove unused imports from dependencies.py
- Fix import sorting across multiple files
- Apply ruff auto-fixes

No functional changes

src/notebooklm_agent/__init__.py

@@ -16,10 +16,10 @@ __author__ = "NotebookLM Agent Team"
 # Core exports
 from notebooklm_agent.core.config import Settings
 from notebooklm_agent.core.exceptions import (
-    NotebookLMAgentError,
-    ValidationError,
     AuthenticationError,
+    NotebookLMAgentError,
     NotFoundError,
+    ValidationError,
 )
 
 __all__ = [

src/notebooklm_agent/api/dependencies.py

@@ -1,13 +1,11 @@
 """FastAPI dependencies for NotebookLM Agent API."""
 
-from functools import lru_cache
 from typing import Annotated
 
-from fastapi import Depends, Header, HTTPException, status
+from fastapi import Depends, HTTPException, status
 from fastapi.security import APIKeyHeader
 
 from notebooklm_agent.core.config import Settings, get_settings
-from notebooklm_agent.core.exceptions import AuthenticationError
 
 # Security scheme
 api_key_header = APIKeyHeader(name="X-API-Key", auto_error=False)

src/notebooklm_agent/api/models/requests.py

@@ -4,9 +4,7 @@ This module contains Pydantic models for API request validation.
 All models use Pydantic v2 syntax.
 """
 
-from datetime import datetime
 from typing import Any
-from uuid import UUID
 
 from pydantic import BaseModel, ConfigDict, Field, field_validator
 

src/notebooklm_agent/api/routes/health.py

@@ -3,7 +3,7 @@
 from datetime import datetime
 from typing import Any
 
-from fastapi import APIRouter, status
+from fastapi import APIRouter
 
 router = APIRouter()
 

src/notebooklm_agent/core/config.py

@@ -66,7 +66,7 @@ class Settings(BaseSettings):
         return not self.debug and not self.testing
 
 
-@lru_cache()
+@lru_cache
 def get_settings() -> Settings:
     """Get cached settings instance.
 

src/notebooklm_agent/core/logging.py

@@ -2,7 +2,6 @@
 
 import logging
 import sys
-from typing import Any
 
 import structlog
 

src/notebooklm_agent/services/notebook_service.py

@@ -8,7 +8,6 @@ from datetime import datetime
 from typing import Any
 from uuid import UUID
 
-from notebooklm_agent.api.models.requests import NotebookCreate, NotebookUpdate
 from notebooklm_agent.api.models.responses import Notebook, PaginatedNotebooks, PaginationMeta
 from notebooklm_agent.core.exceptions import NotebookLMError, NotFoundError, ValidationError