Migrate to Tailwind CSS v4 PostCSS architecture

[Copilot]

Tailwind CSS v4 moved the PostCSS plugin to a separate package @tailwindcss/postcss. The build was failing with:

[postcss] It looks like you're trying to use `tailwindcss` directly as a PostCSS plugin.
The PostCSS plugin has moved to a separate package

Changes

PostCSS Configuration

• Install @tailwindcss/postcss package across workspace
• Update postcss.config.js files to reference @tailwindcss/postcss instead of tailwindcss

CSS Syntax Migration

• Replace @tailwind directives with @import "tailwindcss" (v4 syntax)
• Replace @apply border-border with border-color: hsl(var(--border)) where @apply references custom theme values
• Maintain existing CSS custom properties for theming

Example:

- @tailwind base;
- @tailwind components;
- @tailwind utilities;
+ @import "tailwindcss";

  @layer base {
    * {
-     @apply border-border;
+     border-color: hsl(var(--border));
    }
  }

Package Dependencies

• Update peerDependencies to support both v3 and v4: "tailwindcss": "^3.0.0 || ^4.0.0"

Original prompt

引用: https://github.com/objectstack-ai/objectui/actions/runs/21031227714/job/60467556908#step:6:1

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