fix: sd-datepicker missing read-only attribute/state from Figma

[coraliefeil]

Current behavior

sd-datepicker does not support a read-only state/attribute in code, even though it is defined in Figma.

Expected behavior

sd-datepicker should expose a readonly attribute/state that matches the design defined in Figma, so the component is consistent between design and code (see sd-datepicker docs).

Steps to reproduce

1. Open the Figma component and note the read-only variant
2. Open the sd-datepicker docs page
3. Check available attributes/props
4. Observe that no read-only attribute/state exists in code

Technical Information

• Component: sd-datepicker
• Design reference: Figma – read-only variant
• Code reference: sd-datepicker docs

DoR

• Item has business value
• Item has been estimated by the team
• Item is clear and well-defined
• Item dependencies have been identified