refactor: improve code structure and optimize key functions

backend/app/core/config.py

@@ -0,0 +1,22 @@
+from functools import lru_cache
+from typing import Literal
+
+from pydantic import Field
+from pydantic_settings import BaseSettings, SettingsConfigDict
+
+
+class Settings(BaseSettings):
+    model_config = SettingsConfigDict(env_file=".env", env_file_encoding="utf-8", extra="ignore")
+
+    DATABASE_URL: str = Field(default="postgresql+asyncpg://postgres:postgres@db:5432/ctms")
+    ENV: Literal["development", "production", "test"] = "development"
+    JWT_SECRET_KEY: str = "dev-secret"
+    JWT_EXPIRE_MINUTES: int = 60
+
+
+@lru_cache
+def get_settings() -> Settings:
+    return Settings()
+
+
+settings = get_settings()