feat(extension-sdk): add tailwind vite plugin to vite config

[JammingBen]

This eliminates the need for each extension to do that on its own.

Also fixes the Tailwind import paths in the design-system docs and adds the missing css custom file.

refs opencloud-eu/web-extensions#208

[Copilot]

Pull Request Overview

Adds Tailwind CSS Vite plugin integration to the extension SDK and corrects documentation import paths for the design system. This enables better Tailwind CSS support in extensions while fixing broken import references in the documentation.

• Integrates @tailwindcss/vite plugin into the extension SDK's Vite configuration
• Updates design system documentation to use correct import paths for Tailwind CSS
• Adds missing CSS file copy configuration to the design system build

Reviewed Changes

Copilot reviewed 5 out of 6 changed files in this pull request and generated no comments.

Show a summary per file

File	Description
packages/extension-sdk/package.json	Adds @tailwindcss/vite dependency
packages/extension-sdk/index.mjs	Imports and configures Tailwind Vite plugin
packages/design-system/vite.config.ts	Adds defaults.css file to build output
packages/design-system/docs/gettingStarted/tailwindMigration.md	Fixes Tailwind CSS import path
packages/design-system/docs/gettingStarted/installation.md	Updates import path and removes outdated note

Files not reviewed (1)

• pnpm-lock.yaml: Language not supported

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