fix: resolve Windows "Can't resolve tailwindcss" error (#11747)

On Windows, turbopack/utoopack passes a doubled relative path as the
PostCSS `from` option (e.g. `./Desktop/demo/project/src/file.css`
instead of `./src/file.css`), causing `@tailwindcss/postcss` to resolve
`@import "tailwindcss"` from a non-existent directory.

Add a lightweight PostCSS plugin that detects the broken path (file does
not exist) and corrects it before `@tailwindcss/postcss` reads it.
On macOS/Linux the plugin is a no-op.

Also fix `@source "./src"` → `@source "."` in `src/tailwind.css`:
`@source` paths are relative to the CSS file, so `./src` resolved to
the non-existent `src/src/` directory.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

postcss.config.js

@@ -1,5 +1,35 @@
-module.exports = {
-  plugins: {
-    '@tailwindcss/postcss': {},
+const path = require('path');
+const fs = require('fs');
+
+/**
+ * Workaround for turbopack Windows path doubling bug.
+ * On Windows, turbopack may pass a doubled relative path as the `from` option
+ * to PostCSS (e.g. `./Desktop/demo/project/src/file.css` instead of `./src/file.css`),
+ * causing `path.resolve(cwd, from)` to produce a non-existent doubled path.
+ * This plugin detects and corrects the path before @tailwindcss/postcss reads it.
+ * @see https://github.com/ant-design/ant-design-pro/issues/11747
+ */
+const fixWindowsPathPlugin = {
+  postcssPlugin: 'fix-turbopack-windows-path',
+  Once(_root, { result }) {
+    const from = result.opts.from;
+    if (!from || fs.existsSync(from)) return;
+
+    const cwd = process.cwd();
+    const resolved = path.resolve(from);
+    const relative = path.relative(cwd, resolved);
+    const parts = relative.split(path.sep);
+
+    for (let i = 1; i < parts.length; i++) {
+      const candidate = path.join(cwd, ...parts.slice(i));
+      if (fs.existsSync(candidate)) {
+        result.opts.from = candidate;
+        return;
+      }
+    }
   },
 };
+
+module.exports = {
+  plugins: [fixWindowsPathPlugin, require('@tailwindcss/postcss')],
+};

src/tailwind.css

@@ -1,3 +1,3 @@
 @import "tailwindcss";
 
-@source "./src";
+@source ".";