[marketing] Add Chinese content quality / anti-AI-slop skill

The marketing plugin currently has great skills for content creation, campaign planning, and SEO — but nothing for **content quality control**, especially for non-English content.

Chinese AI-generated content has distinct telltale patterns that are different from English (different filler phrases, punctuation habits, structural clichés). As more teams use Claude for Chinese content marketing, a quality check skill would be valuable.

I've built an open-source skill for this: [stop-slop-zh](https://github.com/pencil20388-eng/stop-slop-zh)

It includes:
- 30+ banned Chinese AI filler phrases
- Punctuation rules specific to Chinese typography (AI overuses colons, em-dashes, double quotes)
- 50+ recommended colloquial expressions for natural voice
- 4-layer quality check system (hard rules → style → content → human-feel)
- Before/after transformation examples

Happy to adapt this into the plugin format if the team thinks it's a good fit for the marketing plugin. Could also work as a standalone `content-quality` or `localization` plugin.