fix(seo): add trailing slash to homepage canonical/hreflang URLs (#235)

Semrush flagged 9 hreflang conflicts on locale homepages (/en/, /de/,
/es/, /pt-BR/) because canonical and hreflang tags pointed to /en
(no trailing slash) while the page is served at /en/ (with trailing
slash). This caused "Conflicting hreflang and rel=canonical" and
"No self-referencing hreflang" errors.

Fix: append trailing slash to path and subPath when mdxPath is empty
(homepage). Deep page URLs are unchanged.

Co-authored-by: paperclip-resolver[bot] <3736210+paperclip-resolver[bot]@users.noreply.github.com>

Author: Mlaz-code

app/[lang]/[[...mdxPath]]/page.tsx

@@ -10,8 +10,8 @@ const DEFAULT_LOCALE = 'en'
 export async function generateMetadata(props) {
   const params = await props.params
   const { metadata } = await importPage(params.mdxPath, params.lang)
-  const path = params.mdxPath ? `/${params.lang}/${params.mdxPath.join('/')}` : `/${params.lang}`
-  const subPath = params.mdxPath ? `/${params.mdxPath.join('/')}` : ''
+  const path = params.mdxPath ? `/${params.lang}/${params.mdxPath.join('/')}` : `/${params.lang}/`
+  const subPath = params.mdxPath ? `/${params.mdxPath.join('/')}` : '/'
   const languages: Record<string, string> = {}
   for (const l of LOCALES) {
     languages[l] = `https://docs.sharpapi.io/${l}${subPath}`