Redirects: add redirect for weird language issue

[Blargian]

Summary

Google Search Console reports many links which aren't indexed or served on Google such as:

• https://clickhouse.com/docs/zh/jp/sql-reference/aggregate-functions/reference/uniqcombined64
• https://clickhouse.com/docs/zh/en/sql-reference/functions/geo/polygons
• https://clickhouse.com/docs/zh/ru/sql-reference/aggregate-functions/reference/last_value
• https://clickhouse.com/docs/zh/en/best-practices/selecting-an-insert-strategy
  etc

Adds a redirect to the correct path based on the first language code. e.g. https://clickhouse.com/docs/zh/en/sql-reference/functions/geo/polygons -> - https://clickhouse.com/docs/zh/sql-reference/functions/geo/polygons

Checklist

• Delete items not relevant to your PR
• URL changes should add a redirect to the old URL via https://github.com/ClickHouse/clickhouse-docs/blob/main/docusaurus.config.js
• If adding a new integration page, also add an entry to the integrations list here: https://github.com/ClickHouse/clickhouse-docs/blob/main/docs/integrations/index.mdx

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Project	Deployment	Preview	Comments	Updated (UTC)
clickhouse-docs	Ready	Preview		Oct 7, 2025 11:16am
clickhouse-docs-ru	Error			Oct 7, 2025 11:16am
clickhouse-docs-zh	Ready	Preview	Comment	Oct 7, 2025 11:16am

[Copilot]

Pull Request Overview

Adds a Vercel redirect rule to handle malformed documentation URLs that contain two language codes instead of one. This addresses Google Search Console reporting issues with URLs like /docs/zh/jp/... or /docs/zh/en/... that should redirect to /docs/zh/....

• Added a single redirect rule in vercel.json to capture URLs with double language codes and redirect to the correct path using only the first language code

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[Copilot]

The language code 'jp' should be 'ja' for Japanese. The correct ISO 639-1 language code for Japanese is 'ja', not 'jp'.

[Blargian]

That's true, but we're special.