fix: make redirects locale-aware

[toakiryu]

Description

This PR fixes an issue where top-level redirects were not fully locale-aware.

The site uses an i18n routing structure where the default locale does not have a URL prefix
(e.g. /docs), while non-default locales do (e.g. /ja/docs).
However, the existing redirect rules only covered non-prefixed routes, which caused 404 pages
when navigating the site in non-default languages via the header links or the "Get Started" CTA.

Since Next.js redirects are not locale-aware by default, both route patterns must be handled
explicitly.

What was fixed

Redirect rules were updated to explicitly support both:

• Default locale routes (e.g. /docs, /blog, /examples)
• Locale-prefixed routes (e.g. /:locale/docs, /:locale/blog, /:locale/examples)

This ensures consistent navigation behavior across all supported languages.

Redirect behavior

• /docs → /docs/getting-started
• /:locale/docs → /:locale/docs/getting-started
• /blog → /blog/swr-v1
• /:locale/blog → /:locale/blog/swr-v1
• /examples → /examples/basic
• /:locale/examples → /:locale/examples/basic

Why this change is needed

• The issue only affects non-default locales, making it easy to miss during development.
• It breaks primary navigation and CTAs for localized users.
• The fix aligns with Next.js i18n routing behavior and avoids implicit assumptions about locales.

Checklist

• Adding new page
• Updating existing documentation
• Other updates (routing / redirect fix)

Note:
This description was written with AI assistance.
Please feel free to suggest wording improvements if anything sounds unnatural.

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