Args:
    image_source: Local file path or http(s) URL of the image.
    mode: One of "general" | "ui_screenshot" | "ocr" | "detect".
        - general       structured subject/background/style description
        - ui_screenshot UI element inventory with bbox + confidence
        - ocr           text-only extraction (see ocr_extract for the dedicated tool)
        - detect        object detection with mandatory bbox
    prompt: Optional extra instructions (e.g. "focus on the top-right card").
    temperature: Sampling temperature, default 0.2 (low = less hallucination).

Returns:
    JSON string. Low-confidence claims are tagged with "_flag": "存疑".

Args:
    image_source: Local file path or http(s) URL of the image.
    prompt: Optional extra instructions.
    temperature: Sampling temperature, default 0.2.

Returns:
    JSON: {"texts":[{"text","bbox","confidence"}], "overall_confidence"}.
    Unclear characters are dropped, never guessed.

Conservative by design: prefers false negatives over false positives.

Args:
    image_source: Local file path or http(s) URL of the image.
    prompt: Optional extra instructions (e.g. "only people and vehicles").
    temperature: Sampling temperature, default 0.2.

Returns:
    JSON: {"objects":[{"label","bbox","confidence"}], "overall_confidence"}.