fix(dashboard): course landing page editor section and currency bugs (#768)

* fix(dashboard): course landing page editor section and currency bugs

- Raise currency select z-index so the dropdown is clickable in the
  full-screen editor shell
- Show dashed top/bottom borders and section title on hover and when
  active in EditableLandingSection
- Map hero/header section keys in the course editor preview context

Co-authored-by: Rotimi Best <rotimi-best@users.noreply.github.com>

* fix(ui): format course landing page pricing with Intl currency

Use getCourseCurrencyFormatter (matching dashboard getCurrencyFormatter)
so NGN and USD prices render as proper locale currency strings instead of
raw numbers with a currency code suffix.

Co-authored-by: Rotimi Best <rotimi-best@users.noreply.github.com>

* fix(ui): prefix group class for landing section hover badge

Co-authored-by: Rotimi Best <rotimi-best@users.noreply.github.com>

* fix(ui): remove unused formatCourseCurrency helper

Co-authored-by: Rotimi Best <rotimi-best@users.noreply.github.com>

* refactor: move currency formatter to @cio/utils

Shared course price formatting belongs in @cio/utils, not the UI
package. Dashboard re-exports the helper to keep existing imports.

Co-authored-by: Rotimi Best <rotimi-best@users.noreply.github.com>

---------

apps/dashboard/src/routes/(app)/courses/[id]/landingpage/+page.svelte

@@ -44,10 +44,13 @@
   };
 
   setLandingPageEditContext({
-    selectedKey: () => selectedSectionKey,
-    selectKey: (key) => (selectedSectionKey = key),
-    labelFor: (key) => t.get(`course.navItem.landing_page.editor.title.${key}` as never) || key,
-    iconFor: (key) => sectionIcons[key] ?? HeaderIcon
+    selectedKey: () => (selectedSectionKey === 'header' ? 'hero' : selectedSectionKey),
+    selectKey: (key) => (selectedSectionKey = key === 'hero' ? 'header' : key),
+    labelFor: (key) => {
+      const sectionKey = key === 'hero' ? 'header' : key;
+      return t.get(`course.navItem.landing_page.editor.title.${sectionKey}` as never) || key;
+    },
+    iconFor: (key) => sectionIcons[key === 'hero' ? 'header' : key] ?? HeaderIcon
   });
 
   function syncCourseStore(_courseData: Course) {