Add loading spinner component

[lexasub]

Replace plain "Loading..." text with a nice spinner.

Files: client/src/components/common/Spinner.jsx (new)

Requirements:

• CSS or SVG spinner animation
• Reusable component
• Use in board loading states

[stevedav131207-cell]

Hey , assign this issue to me .... i will work upon it and try to complete it as soon as possible..