Add shadcn/ui dropdown menu component

[cte]

Description

This is for use in the UI for checkpoints.

https://www.loom.com/share/f6ab3ff58fd7436bafc534fc119e0f3c?sid=b3cbd93e-7027-43ac-99c2-05c8b261e95a

Type of change

• Bug fix (non-breaking change which fixes an issue)
• New feature
• Breaking change (fix or feature that would cause existing functionality to not work as expected)
• This change requires a documentation update

How Has This Been Tested?

Checklist:

• My code follows the patterns of this project
• I have performed a self-review of my own code
• I have commented my code, particularly in hard-to-understand areas
• I have made corresponding changes to the documentation

Additional context

Related Issues

Reviewers

---

Important

Add DropdownMenu component using @radix-ui/react-dropdown-menu and update related CSS and Storybook configurations.

• New Feature:
  • Add DropdownMenu component in dropdown-menu.tsx using @radix-ui/react-dropdown-menu.
  • Add DropdownMenu stories in DropdownMenu.stories.tsx.
• Dependencies:
  • Add @radix-ui/react-dropdown-menu and @radix-ui/react-icons to package.json.
• CSS:
  • Update index.css to use custom preflight styles from preflight.css.
  • Add preflight.css for custom CSS resets.
• Storybook:
  • Remove @chromatic-com/storybook and @storybook/addon-onboarding from main.ts and package.json.

^{This description was created by for 684f89c. It will automatically update as commits are pushed.}

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Latest commit: 684f89c

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[ellipsis-dev]

Multiple pseudo-element selectors use triple-colon syntax (e.g. :::after, :::before, :::backdrop, :::file-selector-button). The standard is double-colon (e.g. ::after). Please update these selectors as they may not work consistently across browsers. This applies to similar occurrences (lines 8-11, 282, 291, 308, 317, 326, 334, 338, 372). See our Development Standards: https://www.notion.so/Development-Standards-59febcf8ead647fd9c2ec3f60c22f3df?pvs=4#11869ad2d5818051ae9cefd92c3aac2b