Integration of the dropdown component to the doc and registry

[sc-vijith]

Summary

• Implemented dropdown component in both the registry and demo directories.
• This adds consistent UI and demo usage for dropdown across the project.

Changes

• Implemented context menu component in src/components/ui/dropdown-menu.tsx
• Created demo component for context menu in src/app/demo/[name]/ui/dropdown-menu.tsx
• Tested the dropdown menu compo

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