fix(docs): add fallback chain for geo IP detection

[cc-hearts]

中文版模板 / Chinese template

🤔 This is a ...

• 🆕 New feature
• 🐞 Bug fix
• 📝 Site / documentation improvement
• 📽️ Demo improvement
• 💄 Component style improvement
• 🤖 TypeScript definition improvement
• 📦 Bundle size optimization
• ⚡️ Performance optimization
• ⭐️ Feature enhancement
• 🌐 Internationalization
• 🛠 Refactoring
• 🎨 Code style optimization
• ✅ Test Case
• 🔀 Branch merge
• ⏩ Workflow
• ⌨️ Accessibility improvement
• ❓ Other (about what?)

🔗 Related Issues

None.

💡 Background and Solution

The docs site asks mainland-China visitors whether they want to be redirected to x.antdv-next.cn. The geo lookup relied on a single endpoint, https://v4_dx.boce.com:44433/ipaddr, which is frequently unreachable (non-standard port, unstable availability). Whenever it fails, getChinaMainlandRedirectDecision() returns skip and the redirect prompt never appears for the users it was built for.

This PR replaces the single endpoint with an ordered fallback chain. Each API is tried in turn; the first one that responds successfully decides the outcome, and probing stops there — a successful non-CN result does not fall through to the next provider. If every request fails, the behaviour is unchanged: return skip silently so the page is never blocked.

The chain, in order:

Endpoint	Response	Notes
https://myip.ipip.net	plain text	Domestic service, fast, CORS-friendly. Hong Kong / Macau / Taiwan are excluded, since ipip.net labels them as 中国香港 / 中国澳门 / 中国台湾.
https://api.ip.sb/geoip	JSON country_code	HK / TW / MO are distinct from CN, so no extra filtering is needed.
https://v4_dx.boce.com:44433/ipaddr	JSON data.from	The original endpoint, kept as a last-resort fallback (same API the antdv-next main site uses).

Parsing is now per-API via a parse(text: string) => boolean hook, so each provider owns its own response format, and the timeout was raised from 1200ms to 1500ms per attempt to reduce false negatives on slow connections.

No user-facing API changed — this only affects the docs site's internal geo detection.

📝 Change Log

Language	Changelog
🇺🇸 English	Fix the mainland-China redirect prompt on the docs site not showing when the geo IP endpoint is unreachable, by adding a fallback chain of geo IP providers.
🇨🇳 Chinese	修复文档站点 IP 地理定位接口不可用时，国内站点跳转提示不显示的问题，改为按顺序尝试多个地理定位接口。