Summary

Switching language on a dynamic CMS page now preserves the translated item slug instead of keeping the source-language one, and dynamic-page links resolve to the localized URL. Closes #340.

Changes

• Add buildLocalizedPageUrls utility that resolves translated folder/page/CMS slugs into relative URLs per locale
• Pre-compute these URLs server-side in PageRenderer (only on multi-locale pages with a locale selector) and pass them to LocaleSelector, which now prefers them over naive prefix manipulation
• Use the raw source slug as the default-locale value and per-locale fallback (the current-locale collectionItem values are already translated)
• Translate referenced/ref dynamic-page link slugs to the active locale so buttons/links point to the localized item URL
• Left-align the read-only "Translating" element library to match the real element library
• Move "Manage locales" to the top of the header locale dropdown

Test plan

• Create a project with 2+ locales (e.g. EN default + FR) and a dynamic CMS page with translated slugs
• Visit a CMS item in FR, switch to EN via the locale selector → URL uses the EN translated slug
• Switch back to FR → URL uses the FR translated slug
• Verify a link/button pointing to a CMS item resolves to the localized slug on a non-default locale
• In the builder on a non-default locale, confirm the "Translating" sidebar is aligned with the element library
• Confirm "Manage locales" appears at the top of the locale dropdown