docs(readme): fix Kimi Code subscription link and price

The Kimi Code subscription link had drifted across the 5 README
translations: the English README pointed to https://www.kimi.com/kimiplus/sale
at $0.99, while the Japanese, Korean, Russian, and Simplified Chinese
versions pointed to https://www.kimi.com/membership/pricing with a
referral tracking ID, also at $0.99 with an "only this month" qualifier.

Normalized all 5 to the canonical https://www.kimi.com/code at $19,
preserving each language's localized "Kimi Code Subscription" wording.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

README.zh-cn.md

@@ -142,7 +142,7 @@ Read this and tell me why it's not just another boilerplate: https://raw.githubu
 
 只需以下订阅之一，ultrawork 就能顺畅工作（本项目与它们没有任何关联，纯属个人推荐）：
 - [ChatGPT 订阅 ($20)](https://chatgpt.com/)
-- [Kimi Code 订阅 ($0.99) (*仅限本月*)](https://www.kimi.com/membership/pricing?track_id=5cdeca93-66f0-4d35-aabb-b6df8fcea328)
+- [Kimi Code 订阅 ($19)](https://www.kimi.com/code)
 - [GLM Coding 套餐 ($10)](https://z.ai/subscribe)
 - 如果你能使用按 token 计费的方式，用 kimi 和 gemini 模型花不了多少钱。