fix: 修复 Linux/Mac 命令行编译样式异常问题

问题原因：
- 自定义 postcss.config.js 覆盖了 uni-app 默认配置
- 导致 rpx 单位没有被正确转换

修复方案：
- 在 postcss.config.js 中添加 uni-app 的 postcss 插件
- 降级 postcss 到版本 7 以兼容 postcss-loader 3.x
- 降级 sass 到 1.32.13 以提高兼容性

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

package.json

@@ -20,8 +20,9 @@
 		"css-loader": "^3.6.0",
 		"file-loader": "^6.2.0",
 		"html-webpack-plugin": "^4.5.2",
+		"postcss": "^7.0.39",
 		"postcss-loader": "^3.0.0",
-		"sass": "^1.96.0",
+		"sass": "^1.32.13",
 		"sass-loader": "^10.5.2",
 		"thread-loader": "^2.1.3",
 		"url-loader": "^4.1.1",
@@ -43,6 +44,7 @@
 		"cross-env": "^7.0.3",
 		"mini-types": "*",
 		"postcss-comment": "^2.0.0",
+		"postcss-import": "^12.0.1",
 		"vue-template-compiler": "^2.6.14"
 	},
 	"browserslist": [