Remove print statements executing during openwebui_engine module import

[Copilot]

Addresses feedback from #2 about print statements executing at module import time in engines/openwebui_engine.py.

Changes

• Moved environment variable loading from module-level to __init__ via new _load_env_variables() method
• Removed print statements on lines 25 and 27 that executed during import
• Environment loading now silent; falls back gracefully if python-dotenv not installed

Before:

# Module-level code - executes on import
try:
    from dotenv import load_dotenv
    env_path = Path(__file__).parent.parent / ".env"
    if env_path.exists():
        load_dotenv(env_path)
        print(f"[OpenWebUIEngine] Loaded environment variables from {env_path}")
except ImportError:
    print("[OpenWebUIEngine] Warning: python-dotenv not installed...")

After:

def __init__(self):
    # ... other initialization ...
    self._load_env_variables()

def _load_env_variables(self):
    """Load environment variables from .env file if available."""
    try:
        from dotenv import load_dotenv
        env_path = Path(__file__).parent.parent / ".env"
        if env_path.exists():
            load_dotenv(env_path)
    except ImportError:
        pass  # Environment variables can still be set via OS

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