fix: ensure canonical URLs match actual URLs with locale prefix

- Update [slug]/page.tsx to always include locale in canonical URL
- Update by-oil/page.tsx to use consistent locale prefix
- Update by-concern/page.tsx to use consistent locale prefix
- All canonical URLs now match actual URLs: /{locale}/solutions/{slug}

src/app/[locale]/solutions/[slug]/page.tsx

@@ -35,8 +35,8 @@ export async function generateMetadata({ params }: PageProps): Promise<Metadata>
   const metaTitle = getLocalizedString(page.metaTitle, validLocale);
   const metaDescription = getLocalizedString(page.metaDescription, validLocale);
   const keywords = getLocalizedKeywords(page.seoKeywords, validLocale);
-  const localePrefix = validLocale === DEFAULT_LOCALE ? "" : `/${validLocale}`;
-  const canonicalUrl = `${baseUrl}${localePrefix}/solutions/${page.localizedSlugs[validLocale as "sr" | "en" | "de" | "fr"]}`;
+  const localePrefix = `/${validLocale}`;
+  const canonicalUrl = `${baseUrl}${localePrefix}/solutions/${slug}`;
   
   return {
     title: metaTitle,
@@ -45,7 +45,7 @@ export async function generateMetadata({ params }: PageProps): Promise<Metadata>
     alternates: {
       canonical: canonicalUrl,
       languages: {
-        "sr": `${baseUrl}/solutions/${page.localizedSlugs.sr}`,
+        "sr": `${baseUrl}/sr/solutions/${page.localizedSlugs.sr}`,
         "en": `${baseUrl}/en/solutions/${page.localizedSlugs.en}`,
         "de": `${baseUrl}/de/solutions/${page.localizedSlugs.de}`,
         "fr": `${baseUrl}/fr/solutions/${page.localizedSlugs.fr}`,