Add the most basic card component

[koppen]

For now this is basically just a frame. Going forward I expect us to add more details and functionality in order to implement all of the options of https://flowbite.com/docs/components/card/ - but for now the most basic version is a good start.

[Copilot]

Pull Request Overview

This PR introduces a basic card component that serves as a foundation for implementing Flowbite's card functionality. The component provides a simple frame with basic styling that can display content.

• Adds a new Flowbite::Card component with default styling based on Flowbite design system
• Includes comprehensive test coverage for the component's rendering behavior
• Provides a preview component for demonstration purposes

Reviewed Changes

Copilot reviewed 4 out of 4 changed files in this pull request and generated 2 comments.

File	Description
app/components/flowbite/card.rb	Implements the main Card component with styling and rendering logic
test/components/flowbite/card_test.rb	Adds unit tests to verify card rendering with correct CSS classes
demo/test/components/previews/card_preview.rb	Creates preview component for visual demonstration
CHANGELOG.md	Documents the addition of the basic Card component

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