Build a star rating component

• Renders a configurable number of stars (default 5) with a value and onChange(value) API
• Hovering a star previews that rating; leaving the component restores the saved value
• Clicking a star sets the rating; clicking the current rating again clears it to 0
• A readOnly prop shows the value with no hover or click behaviour
• Keyboard: the group is reachable with Tab, Arrow keys change the value, Home and End jump to 0 and max
• Screen readers announce it as a radio group with labels like "3 out of 5 stars"

Only after every requirement works.

• Half-star precision, chosen by pointer position within a star
• A size prop and theming through CSS custom properties
• Unit tests for hover, click, clear and keyboard behaviour