🔴 Create /executions/session/{id}/running endpoint #989

@router.get("/session/{session_id}/running")
async def get_running_executions(
    session_id: str,
    db: AsyncSession = Depends(get_db),
    current_user: User = Depends(get_current_user),
):
    """Récupérer les exécutions en cours pour une session."""
    result = await db.execute(
        select(ChatExecution)
        .where(
            ChatExecution.session_id == session_id,
            ChatExecution.status.in_(["running", "completed"])
        )
        .order_by(ChatExecution.created_at.desc())
        .limit(10)
    )
    executions = result.scalars().all()
    return {
        "executions": [
            {
                "execution_id": str(e.id),
                "status": e.status,
                "created_at": e.created_at.isoformat(),
                "completed_at": e.completed_at.isoformat() if e.completed_at else None,
            }
            for e in executions
        ]
    }