fix(website): unify "Playground" translation to "演练场" for zh locale

[lora-sys]

📝 Summary

This PR improves the Chinese (Simplified) translation for the "Playground" feature across the website. It unifies inconsistent and literal translations ("游乐场", "沙盒", "演示机") into a more professional and technically accurate term: "演练场".

💡 Reasoning

• Professionalism: "游乐场" (literal translation of "Amusement Park") sounds unprofessional and childish in a software development context.
• Consistency: The terms "沙盒" (Sandbox) and "演示机" were used inconsistently in different sections.
• Community Standard: "演练场" is a widely accepted translation in the Chinese developer community (e.g., TypeScript Playground), accurately conveying a place for testing and practicing code.

✨ Changes

File Path	Original (zh)	New (zh)	Context
navbar.content.ts	沙盒, 前往游乐场	演练场, 前往演练场	Navigation menu title and accessibility label.
page.content.ts	通过此游乐场...	通过此演练场...	Playground page description.
metadata.content.ts	Playground | Intlayer	演练场 | Intlayer	Page metadata title.
ai-ab-testing-section.content.ts	您的产品实验游乐场。	您的产品实验演练场。	AI A/B Testing section heading.
index.content.ts	前往演示机, 点击这里前往演示机	前往演练场, 点击这里前往演练场	Visual Editor section CTA buttons.

✅ Checklist

• Commits follow Conventional Commit format.
• All occurrences of inconsistent Chinese translations for "Playground" have been updated.
• Code has been reviewed for clarity and technical accuracy.
• No abbreviations used in dictionary content.