fix: resolve weapp-tailwindcss src type issues

[sonofmagic]

Summary

• 修复 packages/weapp-tailwindcss/src 在严格 TypeScript 配置下暴露的类型问题
• 清理对应 ESLint 诊断，并补充中文 changeset
• 同步调整 @weapp-tailwindcss/postcss 相关类型声明以满足 exactOptionalPropertyTypes

Testing

• pnpm --filter weapp-tailwindcss exec eslint ./src --max-warnings=0
• pnpm --filter weapp-tailwindcss exec tsc -p tsconfig.json --noEmit --pretty false 2>&1 | rg '^src/'

Notes

• 未过滤的包级 tsc 仍会报告 test/、tools/weapp-tailwindcss-scripts/、../tailwindcss-config、../test-helper 等范围外问题；本 PR 目标是 packages/weapp-tailwindcss/src。

[changeset-bot]

🦋 Changeset detected

Latest commit: 6e73a6d

The changes in this PR will be included in the next version bump.

This PR includes changesets to release 4 packages

Name	Type
weapp-tailwindcss	Patch
@weapp-tailwindcss/postcss	Patch
@weapp-tailwindcss/test-helper	Patch
@weapp-tailwindcss/build-all	Patch

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