feat(api): implement notebook management CRUD endpoints

Implement Sprint 1: Notebook Management CRUD

- Add NotebookService with full CRUD operations
- Add POST /api/v1/notebooks (create notebook)
- Add GET /api/v1/notebooks (list with pagination)
- Add GET /api/v1/notebooks/{id} (get by ID)
- Add PATCH /api/v1/notebooks/{id} (partial update)
- Add DELETE /api/v1/notebooks/{id} (delete)
- Add Pydantic models for requests/responses
- Add custom exceptions (ValidationError, NotFoundError, NotebookLMError)
- Add comprehensive unit tests (31 tests, 97% coverage)
- Add API integration tests (26 tests)
- Fix router prefix duplication
- Fix JSON serialization in error responses

BREAKING CHANGE: None

src/notebooklm_agent/core/config.py

@@ -0,0 +1,76 @@
+"""Core configuration for NotebookLM Agent API."""
+
+from functools import lru_cache
+from typing import Any
+
+from pydantic import Field, field_validator
+from pydantic_settings import BaseSettings, SettingsConfigDict
+
+
+class Settings(BaseSettings):
+    """Application settings loaded from environment variables."""
+
+    model_config = SettingsConfigDict(
+        env_file=".env",
+        env_file_encoding="utf-8",
+        case_sensitive=False,
+        extra="ignore",
+    )
+
+    # API Configuration
+    api_key: str = Field(default="", alias="NOTEBOOKLM_AGENT_API_KEY")
+    webhook_secret: str = Field(default="", alias="NOTEBOOKLM_AGENT_WEBHOOK_SECRET")
+    port: int = Field(default=8000, alias="NOTEBOOKLM_AGENT_PORT")
+    host: str = Field(default="0.0.0.0", alias="NOTEBOOKLM_AGENT_HOST")
+    reload: bool = Field(default=False, alias="NOTEBOOKLM_AGENT_RELOAD")
+
+    # NotebookLM Configuration
+    notebooklm_home: str = Field(default="~/.notebooklm", alias="NOTEBOOKLM_HOME")
+    notebooklm_profile: str = Field(default="default", alias="NOTEBOOKLM_PROFILE")
+
+    # Redis Configuration
+    redis_url: str = Field(default="redis://localhost:6379/0", alias="REDIS_URL")
+
+    # Logging
+    log_level: str = Field(default="INFO", alias="LOG_LEVEL")
+    log_format: str = Field(default="json", alias="LOG_FORMAT")
+
+    # Development
+    debug: bool = Field(default=False, alias="DEBUG")
+    testing: bool = Field(default=False, alias="TESTING")
+
+    # Security
+    cors_origins: list[str] = Field(default_factory=list, alias="CORS_ORIGINS")
+
+    @field_validator("cors_origins", mode="before")
+    @classmethod
+    def parse_cors_origins(cls, v: Any) -> list[str]:
+        """Parse CORS origins from string or list."""
+        if isinstance(v, str):
+            return [origin.strip() for origin in v.split(",") if origin.strip()]
+        return v if v else []
+
+    @field_validator("log_level")
+    @classmethod
+    def validate_log_level(cls, v: str) -> str:
+        """Validate log level is one of the allowed values."""
+        allowed = {"DEBUG", "INFO", "WARNING", "ERROR", "CRITICAL"}
+        v_upper = v.upper()
+        if v_upper not in allowed:
+            raise ValueError(f"log_level must be one of {allowed}")
+        return v_upper
+
+    @property
+    def is_production(self) -> bool:
+        """Check if running in production mode."""
+        return not self.debug and not self.testing
+
+
+@lru_cache()
+def get_settings() -> Settings:
+    """Get cached settings instance.
+
+    Returns:
+        Settings instance loaded from environment.
+    """
+    return Settings()