def _kind_for(ext: str) -> Optional[str]:
    for kind, exts in ALLOWED_EXTENSIONS.items():
        if ext in exts:
            return kind
    return None


def _serialize(att: Attachment) -> dict:
    return {
        "id": att.id,
        "name": att.name,
        "kind": att.kind,
        "filename": att.filename,
        "mime_type": att.mime_type,
        "size_bytes": att.size_bytes,
=== settings list ===
async def list_settings(db: AsyncSession = Depends(get_db),
                        user: User = Depends(get_current_user)):
    """All settings with current values (DB overrides) and metadata for the UI."""
    rows = (await db.execute(
        select(ApplicationSettings).where(ApplicationSettings.key.in_(SETTING_DEFS.keys()))
    )).scalars().all()
    stored = {r.key: r.value for r in rows}
    out = []
    for key, d in SETTING_DEFS.items():
        out.append({
            "key": key,
            "label": d["label"],
            "category": d["category"],
            "type": d["type"],
            "value": stored.get(key, d["default"]),
            "default": d["default"],
            "is_default": key not in stored,
        })
    return {"settings": out}