feat(dashboard): improve student course sidebar navigation (#814)

* docs(prototypes): add course sidebar navigation HTML prototypes

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

* docs(prototypes): add downloadable zip for course sidebar mockups

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

* feat(dashboard): improve student course sidebar navigation

Collapse all sections except the active one for students, show section
completion as counts (e.g. 3/4), and replace the footer progress card with
prev/next controls plus a thin progress bar.

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

* fix(dashboard): address PR review and remove sidebar prototypes

Remove HTML prototype files from the PR. Match content IDs as exact path
segments for active-item resolution, and use content-neutral prev/next labels.

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

* fix(dashboard): keep ClassroomIO brand untranslated in powered-by footer

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

* fix(dashboard): restore progress summary in course sidebar footer

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

* fix(dashboard): move progress bar below summary in sidebar footer

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

* feat(course): add mobile student bottom nav with outline sheet

Implement prototype 3 mobile navigation for course learners: a fixed
bottom bar with progress ring, prev/next controls, and a sheet showing
the progress card plus collapsible course outline with scroll-to-active.

Extends public-course UI primitives (ring bottom nav, collapsible
sidebar sections, mobile sheet progress slot) and wires them into the
authenticated course layout for isCourseLearnerView on lesson/exercise
routes. Hides duplicate header prev/next and progress popover on mobile.

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

* fix(course): address review feedback and exclude prototypes

- Add .coderabbit.yaml and .greptile/config.json to skip prototypes/**
- Document prototypes/ as out-of-scope in AGENTS.md and Greptile rules
- Render locked mobile outline rows without href navigation targets
- Replace nested IconButton in collapsible section trigger with chevron icon
- Reset public-course sidebar section collapse on every mobile sheet reopen

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

---------

packages/storybook/src/molecules/public-course/fixtures.ts

@@ -93,6 +93,27 @@ export const SIDEBAR_FIXTURE: PublicCourseSidebarSection[] = [
   }
 ];
 
+export const LONG_SIDEBAR_FIXTURE: PublicCourseSidebarSection[] = Array.from({ length: 10 }, (_, sectionIndex) => {
+  const sectionNumber = sectionIndex + 1;
+
+  return {
+    id: `section-${sectionNumber}`,
+    title: `Module ${sectionNumber}`,
+    items: Array.from({ length: 4 }, (_, itemIndex) => {
+      const itemNumber = itemIndex + 1;
+      const slug = `module-${sectionNumber}-lesson-${itemNumber}`;
+
+      return {
+        kind: 'lesson' as const,
+        id: `lesson-${sectionNumber}-${itemNumber}`,
+        slug,
+        title: `Lesson ${itemNumber}: Topic ${sectionNumber}.${itemNumber}`,
+        isUnlocked: true
+      };
+    })
+  };
+});
+
 export const LESSON_FIXTURE: PublicLessonViewData = {
   kind: 'lesson',
   title: 'Hallucination & limitations',