feat(extension-sdk): provide default tailwind config

[JammingBen]

Adds a default tailwind config for extensions so they don't need to ship it on their own.

[Copilot]

Pull Request Overview

This PR adds a default Tailwind CSS configuration to the extension-sdk package to simplify extension development by eliminating the need for extensions to ship their own Tailwind configuration.

• Introduces a preconfigured Tailwind CSS file with custom theme variables and prefixed imports
• Updates documentation to explain how to use the provided Tailwind configuration
• Adds guidance about the required ext: prefix for Tailwind classes in extensions

Reviewed Changes

Copilot reviewed 3 out of 3 changed files in this pull request and generated 1 comment.

File	Description
packages/extension-sdk/tailwind.css	Adds default Tailwind configuration with custom theme variables and prefixed imports
packages/extension-sdk/README.md	Documents how to import and use the provided Tailwind CSS configuration
packages/design-system/docs/gettingStarted/tailwindMigration.md	References the extension-sdk Tailwind config and explains the ext: prefix requirement

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