Fixing Environment Variable Errors

# Accessible from frontend (VITE_ prefix required!)
VITE_API_URL=https://api.example.com
VITE_PUBLIC_KEY=pk_test_xxx

# Not accessible from frontend (server-only)
DATABASE_URL=postgres://...
SECRET_KEY=your-secret

# Accessible from frontend (NEXT_PUBLIC_ prefix required!)
NEXT_PUBLIC_API_URL=https://api.example.com

# Server-only
DATABASE_URL=postgres://...

DATABASE_URL=postgres://user:pass@localhost/db
SECRET_KEY=your-secret-key
DEBUG=true

from pydantic_settings import BaseSettings

class Settings(BaseSettings):
    database_url: str
    secret_key: str
    debug: bool = False

    class Config:
        env_file = ".env"

settings = Settings()

# Environment variable files
.env
.env.local
.env.*.local